From 0de9cd10e7c743be9f52669d80df4cc6b31bb8b0 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Mon, 28 Jun 2021 22:11:43 +0200
Subject: [PATCH 01/11] change styler bar code

---
 pandas/io/formats/style.py                  | 199 +++++++++++++-------
 pandas/tests/io/formats/style/test_align.py |   6 +-
 2 files changed, 137 insertions(+), 68 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index 00c18ac261bab..b5e4921254179 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2042,75 +2042,16 @@ def set_properties(self, subset: Subset | None = None, **kwargs) -> Styler:
         values = "".join(f"{p}: {v};" for p, v in kwargs.items())
         return self.applymap(lambda x: values, subset=subset)
 
-    @staticmethod
-    def _bar(
-        s,
-        align: str,
-        colors: list[str],
-        width: float = 100,
-        vmin: float | None = None,
-        vmax: float | None = None,
-    ):
-        """
-        Draw bar chart in dataframe cells.
-        """
-        # Get input value range.
-        smin = np.nanmin(s.to_numpy()) if vmin is None else vmin
-        smax = np.nanmax(s.to_numpy()) if vmax is None else vmax
-        if align == "mid":
-            smin = min(0, smin)
-            smax = max(0, smax)
-        elif align == "zero":
-            # For "zero" mode, we want the range to be symmetrical around zero.
-            smax = max(abs(smin), abs(smax))
-            smin = -smax
-        # Transform to percent-range of linear-gradient
-        normed = width * (s.to_numpy(dtype=float) - smin) / (smax - smin + 1e-12)
-        zero = -width * smin / (smax - smin + 1e-12)
-
-        def css_bar(start: float, end: float, color: str) -> str:
-            """
-            Generate CSS code to draw a bar from start to end.
-            """
-            css = "width: 10em; height: 80%;"
-            if end > start:
-                css += "background: linear-gradient(90deg,"
-                if start > 0:
-                    css += f" transparent {start:.1f}%, {color} {start:.1f}%, "
-                e = min(end, width)
-                css += f"{color} {e:.1f}%, transparent {e:.1f}%)"
-            return css
-
-        def css(x):
-            if pd.isna(x):
-                return ""
-
-            # avoid deprecated indexing `colors[x > zero]`
-            color = colors[1] if x > zero else colors[0]
-
-            if align == "left":
-                return css_bar(0, x, color)
-            else:
-                return css_bar(min(x, zero), max(x, zero), color)
-
-        if s.ndim == 1:
-            return [css(x) for x in normed]
-        else:
-            return DataFrame(
-                [[css(x) for x in row] for row in normed],
-                index=s.index,
-                columns=s.columns,
-            )
-
     def bar(
         self,
         subset: Subset | None = None,
         axis: Axis | None = 0,
         color="#d65f5f",
         width: float = 100,
-        align: str = "left",
+        align: str | float | int | callable = "left",
         vmin: float | None = None,
         vmax: float | None = None,
+        base_css: str = "width: 10em;",
     ) -> Styler:
         """
         Draw bar chart in the cell backgrounds.
@@ -2154,8 +2095,8 @@ def bar(
         -------
         self : Styler
         """
-        if align not in ("left", "zero", "mid"):
-            raise ValueError("`align` must be one of {'left', 'zero',' mid'}")
+        # if align not in ("left", "zero", "mid"):
+        #     raise ValueError("`align` must be one of {'left', 'zero',' mid'}")
 
         if not (is_list_like(color)):
             color = [color, color]
@@ -2172,14 +2113,15 @@ def bar(
             subset = self.data.select_dtypes(include=np.number).columns
 
         self.apply(
-            self._bar,
+            _bar,
             subset=subset,
             axis=axis,
             align=align,
             colors=color,
-            width=width,
+            width=width / 100,
             vmin=vmin,
             vmax=vmax,
+            base_css=base_css,
         )
 
         return self
@@ -2815,3 +2757,130 @@ def _highlight_between(
         else np.full(data.shape, True, dtype=bool)
     )
     return np.where(g_left & l_right, props, "")
+
+
+def _bar(
+    data: FrameOrSeries,
+    align: str | float | int | callable,
+    colors: list[str],
+    width: float,
+    vmin: float,
+    vmax: float,
+    base_css: str,
+):
+    """
+    Draw bar chart in dataframe cells.
+    """
+
+    def css_bar(base_css: str, start: float, end: float, color: str) -> str:
+        """
+        Generate CSS code to draw a bar from start to end in a table cell.
+
+        Uses linear-gradient.
+
+        Parameters
+        ----------
+        base_css : str
+            Additional CSS applied to cell as well as linear gradient.
+        start : float
+            Relative positional start of bar coloring in [0,1]
+        end : float
+            Relative positional end of the bar coloring in [0,1]
+        color : str
+            CSS valid color to apply.
+
+        Returns
+        -------
+        str : The CSS applicable to the cell.
+        """
+        if end > start:
+            base_css += "background: linear-gradient(90deg,"
+            if start > 0:
+                base_css += f" transparent {start*100:.1f}%, {color} {start*100:.1f}%, "
+            base_css += f"{color} {end*100:.1f}%, transparent {end*100:.1f}%)"
+        return base_css
+
+    def css_calc(x, left: float, right: float, align: str, width: float):
+        """
+        Return the correct CSS for bar placement based on calculated values.
+
+        Parameters
+        ----------
+        x : float
+            Value which determines the bar placement.
+        left : float
+            Value marking the left side of calculation.
+        right : float
+            Value marking the right side of the calculation (left < right).
+        align : {"left", "right", "zero"}
+            How the bars will be positioned. Note if using "zero" with an adjustment
+            such as a mean, ensure ``left`` and ``right`` are also adjusted on input.
+        width : float
+            The proportionate width of the cell to take up in [0,1]. Measured according
+            to ``align``.
+
+        Returns
+        -------
+        str : Resultant CSS with linear gradient.
+        """
+        if pd.isna(x):
+            return ""
+
+        color = colors[0] if x < 0 else colors[1]
+        x = left if x < left else x
+        x = right if x > right else x
+
+        if align == "left":
+            end = (x - left) / (right - left)
+            return css_bar(base_css, 0, end * width, color)
+        elif align == "right":
+            start = (x - left) / (right - left)
+            return css_bar(base_css, (1 - width) + start * width, 1, color)
+        elif align == "zero":
+            if right < 0:
+                right = -left  # since abs(right) < abs(left)
+            elif left > 0:
+                left = -right  # since abs(left) < abs(right)
+            elif abs(right) < abs(left):
+                right = -left  # apparent
+            else:
+                left = -right
+
+            if x < 0:
+                start = (x - left) / (right - left)
+                return css_bar(base_css, (1 - width) / 2 + start * width, 0.5, color)
+            else:
+                end = (x - 0) / (right - left)
+                return css_bar(base_css, 0.5, end * width + 0.5, color)
+
+    values = data.to_numpy()
+    left = np.nanmin(values) if vmin is None else vmin
+    right = np.nanmax(values) if vmax is None else vmax
+
+    if align == "mid":
+        z, align = (left + right) / 2, "zero"
+    elif align == "mean":
+        z, align = np.nanmean(values), "zero"
+    elif callable(align):
+        z, align = align(values), "zero"
+    elif isinstance(align, (float, int)):
+        z, align = float(align), "zero"
+    elif align == "left" or align == "right" or align == "zero":
+        z = 0
+    else:
+        raise ValueError(
+            "`align` should be in {'left', 'right', 'mid', 'mean', 'zero'} or be a "
+            "value defining the center line or a callable that returns a float"
+        )
+
+    if data.ndim == 1:
+        return [css_calc(x - z, left - z, right - z, align, width) for x in values]
+    else:
+        return DataFrame(
+            [
+                [css_calc(x - z, left - z, right - z, align, width) for x in row]
+                for row in values
+            ],
+            index=data.index,
+            columns=data.columns,
+        )
diff --git a/pandas/tests/io/formats/style/test_align.py b/pandas/tests/io/formats/style/test_align.py
index f81c1fbd6d85e..00ea05ea67506 100644
--- a/pandas/tests/io/formats/style/test_align.py
+++ b/pandas/tests/io/formats/style/test_align.py
@@ -7,7 +7,7 @@
 
 def bar_grad(a=None, b=None, c=None, d=None):
     """Used in multiple tests to simplify formatting of expected result"""
-    ret = [("width", "10em"), ("height", "80%")]
+    ret = [("width", "10em")]
     if all(x is None for x in [a, b, c, d]):
         return ret
     return ret + [
@@ -401,6 +401,6 @@ def test_bar_align_zero_nans(self):
 
     def test_bar_bad_align_raises(self):
         df = DataFrame({"A": [-100, -60, -30, -20]})
-        msg = "`align` must be one of {'left', 'zero',' mid'}"
+        msg = "`align` should be in {'left', 'right', 'mid', 'mean', 'zero'} or"
         with pytest.raises(ValueError, match=msg):
-            df.style.bar(align="poorly", color=["#d65f5f", "#5fba7d"])
+            df.style.bar(align="poorly", color=["#d65f5f", "#5fba7d"]).render()

From 9addb866f80fea45948a1bae55b9a54c7051223a Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Mon, 28 Jun 2021 23:56:30 +0200
Subject: [PATCH 02/11] width centralised

---
 pandas/io/formats/style.py | 51 +++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index b5e4921254179..f4598861ac4d5 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2812,7 +2812,7 @@ def css_calc(x, left: float, right: float, align: str, width: float):
             Value marking the left side of calculation.
         right : float
             Value marking the right side of the calculation (left < right).
-        align : {"left", "right", "zero"}
+        align : {"left", "right", "zero", "mid"}
             How the bars will be positioned. Note if using "zero" with an adjustment
             such as a mean, ensure ``left`` and ``right`` are also adjusted on input.
         width : float
@@ -2828,37 +2828,60 @@ def css_calc(x, left: float, right: float, align: str, width: float):
 
         color = colors[0] if x < 0 else colors[1]
         x = left if x < left else x
-        x = right if x > right else x
+        x = right if x > right else x  # trim data if outside of the window
 
         if align == "left":
-            end = (x - left) / (right - left)
-            return css_bar(base_css, 0, end * width, color)
+            # all proportions are measured from the left side between left and right
+            start, end = 0, (x - left) / (right - left) * width
+
         elif align == "right":
-            start = (x - left) / (right - left)
-            return css_bar(base_css, (1 - width) + start * width, 1, color)
+            # all proportions are measured from the right side between left and right
+            start, end = (1 - width) + (x - left) / (right - left) * width, 1
+
         elif align == "zero":
+            # all proportions are measured from the center which is set to zero
+            # input data will have been translated if centering about a mean for example
             if right < 0:
-                right = -left  # since abs(right) < abs(left)
-            elif left > 0:
-                left = -right  # since abs(left) < abs(right)
+                right = -left  # since abs(right) < abs(left): all data below zero
+            elif left >= 0:
+                left = -right  # since abs(left) < abs(right): all data above zero
             elif abs(right) < abs(left):
-                right = -left  # apparent
+                right = -left  # standardise left and right as same distance from zero
             else:
                 left = -right
 
+            if x < 0:
+                start, end = (1 - width) / 2 + width * (x - left) / (right - left), 0.5
+            else:
+                start, end = 0.5, x / (right - left) * width + 0.5
+
+        elif align == "mid":
+            mid = (left + right) / 2
+            if mid < 0:
+                zero_frac = (0 - mid) / (right - mid) + 0.5
+            else:
+                zero_frac = (0 - left) / (right - left)
+
             if x < 0:
                 start = (x - left) / (right - left)
-                return css_bar(base_css, (1 - width) / 2 + start * width, 0.5, color)
+                end = zero_frac
             else:
-                end = (x - 0) / (right - left)
-                return css_bar(base_css, 0.5, end * width + 0.5, color)
+                start = zero_frac
+                end = (x - left) / (right - left)
+
+        return css_bar(base_css, start, end, color)
 
     values = data.to_numpy()
     left = np.nanmin(values) if vmin is None else vmin
     right = np.nanmax(values) if vmax is None else vmax
 
     if align == "mid":
-        z, align = (left + right) / 2, "zero"
+        if all(values >= 0):  # "mid" is documented to act as "left" if all positive
+            z, align, left = 0, "left", 0 if vmin is None else vmin
+        elif all(values <= 0):  # "mid" is documented to act as "right" if all negative
+            z, align, right = 0, "right", 0 if vmax is None else vmax
+        else:
+            z = 0
     elif align == "mean":
         z, align = np.nanmean(values), "zero"
     elif callable(align):

From 54a7813875cbe3deaa95e261371b4606c9a7f016 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 00:11:01 +0200
Subject: [PATCH 03/11] align with existing tests

---
 pandas/io/formats/style.py | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index f4598861ac4d5..8f1928ca4b5f5 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2832,11 +2832,11 @@ def css_calc(x, left: float, right: float, align: str, width: float):
 
         if align == "left":
             # all proportions are measured from the left side between left and right
-            start, end = 0, (x - left) / (right - left) * width
+            start, end = 0, (x - left) / (right - left)
 
         elif align == "right":
             # all proportions are measured from the right side between left and right
-            start, end = (1 - width) + (x - left) / (right - left) * width, 1
+            start, end = (x - left) / (right - left), 1
 
         elif align == "zero":
             # all proportions are measured from the center which is set to zero
@@ -2851,14 +2851,14 @@ def css_calc(x, left: float, right: float, align: str, width: float):
                 left = -right
 
             if x < 0:
-                start, end = (1 - width) / 2 + width * (x - left) / (right - left), 0.5
+                start, end = (x - left) / (right - left), 0.5
             else:
-                start, end = 0.5, x / (right - left) * width + 0.5
+                start, end = 0.5, x / (right - left) + 0.5
 
         elif align == "mid":
             mid = (left + right) / 2
             if mid < 0:
-                zero_frac = (0 - mid) / (right - mid) + 0.5
+                zero_frac = (0 - mid) / (right - left) + 0.5
             else:
                 zero_frac = (0 - left) / (right - left)
 
@@ -2869,16 +2869,16 @@ def css_calc(x, left: float, right: float, align: str, width: float):
                 start = zero_frac
                 end = (x - left) / (right - left)
 
-        return css_bar(base_css, start, end, color)
+        return css_bar(base_css, start * width, end * width, color)
 
     values = data.to_numpy()
     left = np.nanmin(values) if vmin is None else vmin
     right = np.nanmax(values) if vmax is None else vmax
 
     if align == "mid":
-        if all(values >= 0):  # "mid" is documented to act as "left" if all positive
+        if np.all(values >= 0):  # "mid" is documented to act as "left" if all positive
             z, align, left = 0, "left", 0 if vmin is None else vmin
-        elif all(values <= 0):  # "mid" is documented to act as "right" if all negative
+        elif np.all(values <= 0):  # "mid" is documented to act as "right" if all neg
             z, align, right = 0, "right", 0 if vmax is None else vmax
         else:
             z = 0

From 50eff0fa61b9c613e90fa04e3afafae66254047b Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 00:18:18 +0200
Subject: [PATCH 04/11] fix formattimg and tests

---
 pandas/io/formats/style.py                  |  4 +-
 pandas/tests/io/formats/style/test_align.py | 58 ++++++++++-----------
 2 files changed, 31 insertions(+), 31 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index 8f1928ca4b5f5..cc2453a2c801f 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2796,8 +2796,8 @@ def css_bar(base_css: str, start: float, end: float, color: str) -> str:
         if end > start:
             base_css += "background: linear-gradient(90deg,"
             if start > 0:
-                base_css += f" transparent {start*100:.1f}%, {color} {start*100:.1f}%, "
-            base_css += f"{color} {end*100:.1f}%, transparent {end*100:.1f}%)"
+                base_css += f" transparent {start*100:.1f}%, {color} {start*100:.1f}%,"
+            base_css += f" {color} {end*100:.1f}%, transparent {end*100:.1f}%)"
         return base_css
 
     def css_calc(x, left: float, right: float, align: str, width: float):
diff --git a/pandas/tests/io/formats/style/test_align.py b/pandas/tests/io/formats/style/test_align.py
index 00ea05ea67506..209370825444d 100644
--- a/pandas/tests/io/formats/style/test_align.py
+++ b/pandas/tests/io/formats/style/test_align.py
@@ -24,16 +24,16 @@ def test_bar_align_left(self):
         result = df.style.bar()._compute().ctx
         expected = {
             (0, 0): bar_grad(),
-            (1, 0): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (2, 0): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
+            (1, 0): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (2, 0): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
         }
         assert result == expected
 
         result = df.style.bar(color="red", width=50)._compute().ctx
         expected = {
             (0, 0): bar_grad(),
-            (1, 0): bar_grad("red 25.0%", " transparent 25.0%"),
-            (2, 0): bar_grad("red 50.0%", " transparent 50.0%"),
+            (1, 0): bar_grad(" red 25.0%", " transparent 25.0%"),
+            (2, 0): bar_grad(" red 50.0%", " transparent 50.0%"),
         }
         assert result == expected
 
@@ -51,26 +51,26 @@ def test_bar_align_left_0points(self):
             (0, 0): bar_grad(),
             (0, 1): bar_grad(),
             (0, 2): bar_grad(),
-            (1, 0): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (1, 1): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (1, 2): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (2, 0): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
-            (2, 1): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
-            (2, 2): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
+            (1, 0): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (1, 1): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (1, 2): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (2, 0): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
+            (2, 1): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
+            (2, 2): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
         }
         assert result == expected
 
         result = df.style.bar(axis=1)._compute().ctx
         expected = {
             (0, 0): bar_grad(),
-            (0, 1): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (0, 2): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
+            (0, 1): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (0, 2): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
             (1, 0): bar_grad(),
-            (1, 1): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (1, 2): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
+            (1, 1): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (1, 2): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
             (2, 0): bar_grad(),
-            (2, 1): bar_grad("#d65f5f 50.0%", " transparent 50.0%"),
-            (2, 2): bar_grad("#d65f5f 100.0%", " transparent 100.0%"),
+            (2, 1): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
+            (2, 2): bar_grad(" #d65f5f 100.0%", " transparent 100.0%"),
         }
         assert result == expected
 
@@ -79,7 +79,7 @@ def test_bar_align_mid_pos_and_neg(self):
         result = df.style.bar(align="mid", color=["#d65f5f", "#5fba7d"])._compute().ctx
         expected = {
             (0, 0): bar_grad(
-                "#d65f5f 10.0%",
+                " #d65f5f 10.0%",
                 " transparent 10.0%",
             ),
             (1, 0): bar_grad(),
@@ -105,19 +105,19 @@ def test_bar_align_mid_all_pos(self):
 
         expected = {
             (0, 0): bar_grad(
-                "#5fba7d 10.0%",
+                " #5fba7d 10.0%",
                 " transparent 10.0%",
             ),
             (1, 0): bar_grad(
-                "#5fba7d 20.0%",
+                " #5fba7d 20.0%",
                 " transparent 20.0%",
             ),
             (2, 0): bar_grad(
-                "#5fba7d 50.0%",
+                " #5fba7d 50.0%",
                 " transparent 50.0%",
             ),
             (3, 0): bar_grad(
-                "#5fba7d 100.0%",
+                " #5fba7d 100.0%",
                 " transparent 100.0%",
             ),
         }
@@ -131,7 +131,7 @@ def test_bar_align_mid_all_neg(self):
 
         expected = {
             (0, 0): bar_grad(
-                "#d65f5f 100.0%",
+                " #d65f5f 100.0%",
                 " transparent 100.0%",
             ),
             (1, 0): bar_grad(
@@ -193,15 +193,15 @@ def test_bar_align_left_axis_none(self):
         expected = {
             (0, 0): bar_grad(),
             (1, 0): bar_grad(
-                "#d65f5f 25.0%",
+                " #d65f5f 25.0%",
                 " transparent 25.0%",
             ),
             (0, 1): bar_grad(
-                "#d65f5f 50.0%",
+                " #d65f5f 50.0%",
                 " transparent 50.0%",
             ),
             (1, 1): bar_grad(
-                "#d65f5f 100.0%",
+                " #d65f5f 100.0%",
                 " transparent 100.0%",
             ),
         }
@@ -245,7 +245,7 @@ def test_bar_align_mid_axis_none(self):
                 " transparent 50.0%",
             ),
             (0, 1): bar_grad(
-                "#d65f5f 33.3%",
+                " #d65f5f 33.3%",
                 " transparent 33.3%",
             ),
             (1, 1): bar_grad(
@@ -295,7 +295,7 @@ def test_bar_align_mid_vmax(self):
                 " transparent 30.0%",
             ),
             (0, 1): bar_grad(
-                "#d65f5f 20.0%",
+                " #d65f5f 20.0%",
                 " transparent 20.0%",
             ),
             (1, 1): bar_grad(
@@ -344,7 +344,7 @@ def test_bar_align_mid_vmin_vmax_clipping(self):
                 " #d65f5f 50.0%",
                 " transparent 50.0%",
             ),
-            (0, 1): bar_grad("#d65f5f 25.0%", " transparent 25.0%"),
+            (0, 1): bar_grad(" #d65f5f 25.0%", " transparent 25.0%"),
             (1, 1): bar_grad(
                 " transparent 25.0%",
                 " #d65f5f 25.0%",
@@ -364,7 +364,7 @@ def test_bar_align_mid_nans(self):
                 " #d65f5f 50.0%",
                 " transparent 50.0%",
             ),
-            (0, 1): bar_grad("#d65f5f 25.0%", " transparent 25.0%"),
+            (0, 1): bar_grad(" #d65f5f 25.0%", " transparent 25.0%"),
             (1, 1): bar_grad(
                 " transparent 25.0%",
                 " #d65f5f 25.0%",

From bcd4914dc8164f80471b8a2f0a1272db13578f9d Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 01:07:31 +0200
Subject: [PATCH 05/11] documentation and amended tests

---
 doc/source/user_guide/style.ipynb           | 22 ++++++-----
 pandas/io/formats/style.py                  | 42 +++++++++++++--------
 pandas/tests/io/formats/style/test_align.py |  2 +
 3 files changed, 42 insertions(+), 24 deletions(-)

diff --git a/doc/source/user_guide/style.ipynb b/doc/source/user_guide/style.ipynb
index 6e10e6ec74b48..4da473e762e92 100644
--- a/doc/source/user_guide/style.ipynb
+++ b/doc/source/user_guide/style.ipynb
@@ -1190,9 +1190,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "In version 0.20.0 the ability to customize the bar chart further was given. You can now have the `df.style.bar` be centered on zero or midpoint value (in addition to the already existing way of having the min value at the left side of the cell), and you can pass a list of `[color_negative, color_positive]`.\n",
+    "Additional keyword arguments give more control on centering and positioning, and you can pass a list of `[color_negative, color_positive]` to highlight lower and higher values.\n",
     "\n",
-    "Here's how you can change the above with the new `align='mid'` option:"
+    "Here's how you can change the above with the new `align` option, combined with setting `vmin` and `vmax` limits, the `width` of the figure, and underlying css `props` of cells, leaving space to display the text and the bars:"
    ]
   },
   {
@@ -1201,7 +1201,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "df2.style.bar(subset=['A', 'B'], align='mid', color=['#d65f5f', '#5fba7d'])"
+    "df2.style.bar(align=0, vmin=-2.5, vmax=2.5, color=['#d65f5f', '#5fba7d'],\n",
+    "              width=60, props=\"width: 120px; border-right: 1px solid black;\").format('{:.3f}', na_rep=\"\")"
    ]
   },
   {
@@ -1225,28 +1226,31 @@
     "\n",
     "# Test series\n",
     "test1 = pd.Series([-100,-60,-30,-20], name='All Negative')\n",
-    "test2 = pd.Series([10,20,50,100], name='All Positive')\n",
-    "test3 = pd.Series([-10,-5,0,90], name='Both Pos and Neg')\n",
+    "test2 = pd.Series([-10,-5,0,90], name='Both Pos and Neg')\n",
+    "test3 = pd.Series([10,20,50,100], name='All Positive')\n",
+    "test4 = pd.Series([100, 103, 101, 102], name='Large Positive')\n",
+    "\n",
     "\n",
     "head = \"\"\"\n",
     "<table>\n",
     "    <thead>\n",
     "        <th>Align</th>\n",
     "        <th>All Negative</th>\n",
-    "        <th>All Positive</th>\n",
     "        <th>Both Neg and Pos</th>\n",
+    "        <th>All Positive</th>\n",
+    "        <th>Large Positive</th>\n",
     "    </thead>\n",
     "    </tbody>\n",
     "\n",
     "\"\"\"\n",
     "\n",
-    "aligns = ['left','zero','mid']\n",
+    "aligns = ['left', 'right', 'zero', 'mid', 'mean', 99]\n",
     "for align in aligns:\n",
     "    row = \"<tr><th>{}</th>\".format(align)\n",
-    "    for series in [test1,test2,test3]:\n",
+    "    for series in [test1,test2,test3, test4]:\n",
     "        s = series.copy()\n",
     "        s.name=''\n",
-    "        row += \"<td>{}</td>\".format(s.to_frame().style.bar(align=align, \n",
+    "        row += \"<td>{}</td>\".format(s.to_frame().style.hide_index().bar(align=align, \n",
     "                                                           color=['#d65f5f', '#5fba7d'], \n",
     "                                                           width=100).render()) #testn['width']\n",
     "    row += '</tr>'\n",
diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index cc2453a2c801f..fc814a97e1900 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2051,7 +2051,7 @@ def bar(
         align: str | float | int | callable = "left",
         vmin: float | None = None,
         vmax: float | None = None,
-        base_css: str = "width: 10em;",
+        props: str = "width: 10em;",
     ) -> Styler:
         """
         Draw bar chart in the cell backgrounds.
@@ -2072,16 +2072,26 @@ def bar(
             first element is the color_negative and the second is the
             color_positive (eg: ['#d65f5f', '#5fba7d']).
         width : float, default 100
-            A number between 0 or 100. The largest value will cover `width`
-            percent of the cell's width.
-        align : {'left', 'zero',' mid'}, default 'left'
-            How to align the bars with the cells.
-
-            - 'left' : the min value starts at the left of the cell.
+            The percentage of the cell, measured from the left, in which to draw the
+            bars, in [0, 100].
+        align : str, int, float, callable, default 'left'
+            How to align the bars within the cells relative to a width adjusted center.
+            If string must be one of:
+
+            - 'left' : bars are drawn rightwards from the minimum data value.
+            - 'right' : bars are drawn leftwards from the maximum data value.
             - 'zero' : a value of zero is located at the center of the cell.
-            - 'mid' : the center of the cell is at (max-min)/2, or
-              if values are all negative (positive) the zero is aligned
-              at the right (left) of the cell.
+            - 'mid' : a value of (max-min)/2 is located at the center of the cell,
+              or if all values are negative (positive) the zero is
+              aligned at the right (left) of the cell.
+            - 'mean' : the mean value of the data is located at the center of the cell.
+
+            If a float or integer is given this will indicate the center of the cell.
+
+            If a callable should take a 1d or 2d array and return a scalar.
+
+            .. versionchanged:: 1.4.0
+
         vmin : float, optional
             Minimum bar value, defining the left hand limit
             of the bar drawing range, lower values are clipped to `vmin`.
@@ -2090,14 +2100,16 @@ def bar(
             Maximum bar value, defining the right hand limit
             of the bar drawing range, higher values are clipped to `vmax`.
             When None (default): the maximum value of the data will be used.
+        props : str, optional
+            The base CSS of the cell that is extended to add the bar chart. Defaults to
+            `"width: 100px;"`
+
+            .. versionadded:: 1.4.0
 
         Returns
         -------
         self : Styler
         """
-        # if align not in ("left", "zero", "mid"):
-        #     raise ValueError("`align` must be one of {'left', 'zero',' mid'}")
-
         if not (is_list_like(color)):
             color = [color, color]
         elif len(color) == 1:
@@ -2121,7 +2133,7 @@ def bar(
             width=width / 100,
             vmin=vmin,
             vmax=vmax,
-            base_css=base_css,
+            base_css=props,
         )
 
         return self
@@ -2824,7 +2836,7 @@ def css_calc(x, left: float, right: float, align: str, width: float):
         str : Resultant CSS with linear gradient.
         """
         if pd.isna(x):
-            return ""
+            return base_css
 
         color = colors[0] if x < 0 else colors[1]
         x = left if x < left else x
diff --git a/pandas/tests/io/formats/style/test_align.py b/pandas/tests/io/formats/style/test_align.py
index 209370825444d..7e74f0d0f304f 100644
--- a/pandas/tests/io/formats/style/test_align.py
+++ b/pandas/tests/io/formats/style/test_align.py
@@ -365,6 +365,7 @@ def test_bar_align_mid_nans(self):
                 " transparent 50.0%",
             ),
             (0, 1): bar_grad(" #d65f5f 25.0%", " transparent 25.0%"),
+            (1, 0): bar_grad(),
             (1, 1): bar_grad(
                 " transparent 25.0%",
                 " #d65f5f 25.0%",
@@ -390,6 +391,7 @@ def test_bar_align_zero_nans(self):
                 " #d65f5f 50.0%",
                 " transparent 50.0%",
             ),
+            (1, 0): bar_grad(),
             (1, 1): bar_grad(
                 " transparent 50.0%",
                 " #d65f5f 50.0%",

From e711c7d223180faeeddd45645ac90080807b3189 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 08:39:20 +0200
Subject: [PATCH 06/11] documentation, refactor, and amended tests

---
 pandas/io/formats/style.py                  | 73 +++++++++++++--------
 pandas/tests/io/formats/style/test_align.py |  4 +-
 2 files changed, 49 insertions(+), 28 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index fc814a97e1900..187231942b866 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2048,7 +2048,7 @@ def bar(
         axis: Axis | None = 0,
         color="#d65f5f",
         width: float = 100,
-        align: str | float | int | callable = "left",
+        align: str | float | int | callable = "mid",
         vmin: float | None = None,
         vmax: float | None = None,
         props: str = "width: 10em;",
@@ -2074,7 +2074,7 @@ def bar(
         width : float, default 100
             The percentage of the cell, measured from the left, in which to draw the
             bars, in [0, 100].
-        align : str, int, float, callable, default 'left'
+        align : str, int, float, callable, default 'mid'
             How to align the bars within the cells relative to a width adjusted center.
             If string must be one of:
 
@@ -2776,15 +2776,32 @@ def _bar(
     align: str | float | int | callable,
     colors: list[str],
     width: float,
-    vmin: float,
-    vmax: float,
+    vmin: float | None,
+    vmax: float | None,
     base_css: str,
 ):
     """
-    Draw bar chart in dataframe cells.
+    Draw bar chart in data cells using HTML CSS linear gradient.
+
+    Parameters
+    ----------
+    data : Series or DataFrame
+        Underling subset of Styler data on which operations are performed.
+    align : str in {"left", "right", "mid", "zero", "mean"}, int, float, callable
+        Method for how bars are structured or scalar value of centre point.
+    colors : list-like of str
+        Two listed colors as string in valid CSS.
+    width : float in [0,1]
+        The percentage of the cell, measured from left, where drawn bars will reside.
+    vmin : float, optional
+        Overwrite the minimum value of the window.
+    vmax : float, optional
+        Overwrite the maximum value of the window.
+    base_css : str
+        Additional CSS that is included in the cell before bars are drawn.
     """
 
-    def css_bar(base_css: str, start: float, end: float, color: str) -> str:
+    def css_bar(start: float, end: float, color: str) -> str:
         """
         Generate CSS code to draw a bar from start to end in a table cell.
 
@@ -2792,8 +2809,6 @@ def css_bar(base_css: str, start: float, end: float, color: str) -> str:
 
         Parameters
         ----------
-        base_css : str
-            Additional CSS applied to cell as well as linear gradient.
         start : float
             Relative positional start of bar coloring in [0,1]
         end : float
@@ -2804,15 +2819,20 @@ def css_bar(base_css: str, start: float, end: float, color: str) -> str:
         Returns
         -------
         str : The CSS applicable to the cell.
+
+        Notes
+        -----
+        Uses ``base_css`` from outer scope.
         """
+        cell_css = base_css
         if end > start:
-            base_css += "background: linear-gradient(90deg,"
+            cell_css += "background: linear-gradient(90deg,"
             if start > 0:
-                base_css += f" transparent {start*100:.1f}%, {color} {start*100:.1f}%,"
-            base_css += f" {color} {end*100:.1f}%, transparent {end*100:.1f}%)"
-        return base_css
+                cell_css += f" transparent {start*100:.1f}%, {color} {start*100:.1f}%,"
+            cell_css += f" {color} {end*100:.1f}%, transparent {end*100:.1f}%)"
+        return cell_css
 
-    def css_calc(x, left: float, right: float, align: str, width: float):
+    def css_calc(x, left: float, right: float, align: str):
         """
         Return the correct CSS for bar placement based on calculated values.
 
@@ -2827,13 +2847,14 @@ def css_calc(x, left: float, right: float, align: str, width: float):
         align : {"left", "right", "zero", "mid"}
             How the bars will be positioned. Note if using "zero" with an adjustment
             such as a mean, ensure ``left`` and ``right`` are also adjusted on input.
-        width : float
-            The proportionate width of the cell to take up in [0,1]. Measured according
-            to ``align``.
 
         Returns
         -------
         str : Resultant CSS with linear gradient.
+
+        Notes
+        -----
+        Uses ``colors`` and ``width`` from outer scope.
         """
         if pd.isna(x):
             return base_css
@@ -2868,20 +2889,20 @@ def css_calc(x, left: float, right: float, align: str, width: float):
                 start, end = 0.5, x / (right - left) + 0.5
 
         elif align == "mid":
+            # bars are drawn from zero either leftwards or rightwards with center of
+            # cell placed at mid
             mid = (left + right) / 2
-            if mid < 0:
-                zero_frac = (0 - mid) / (right - left) + 0.5
+            if mid < 0:  # get the proportionate location of zero where bars start/end
+                zero_frac = -mid / (right - left) + 0.5
             else:
-                zero_frac = (0 - left) / (right - left)
+                zero_frac = -left / (right - left)
 
             if x < 0:
-                start = (x - left) / (right - left)
-                end = zero_frac
+                start, end = (x - left) / (right - left), zero_frac
             else:
-                start = zero_frac
-                end = (x - left) / (right - left)
+                start, end = zero_frac, (x - left) / (right - left)
 
-        return css_bar(base_css, start * width, end * width, color)
+        return css_bar(start * width, end * width, color)
 
     values = data.to_numpy()
     left = np.nanmin(values) if vmin is None else vmin
@@ -2909,11 +2930,11 @@ def css_calc(x, left: float, right: float, align: str, width: float):
         )
 
     if data.ndim == 1:
-        return [css_calc(x - z, left - z, right - z, align, width) for x in values]
+        return [css_calc(x - z, left - z, right - z, align) for x in values]
     else:
         return DataFrame(
             [
-                [css_calc(x - z, left - z, right - z, align, width) for x in row]
+                [css_calc(x - z, left - z, right - z, align) for x in row]
                 for row in values
             ],
             index=data.index,
diff --git a/pandas/tests/io/formats/style/test_align.py b/pandas/tests/io/formats/style/test_align.py
index 7e74f0d0f304f..78fc8051af25c 100644
--- a/pandas/tests/io/formats/style/test_align.py
+++ b/pandas/tests/io/formats/style/test_align.py
@@ -46,7 +46,7 @@ def test_bar_align_left(self):
 
     def test_bar_align_left_0points(self):
         df = DataFrame([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
-        result = df.style.bar()._compute().ctx
+        result = df.style.bar(align="left")._compute().ctx
         expected = {
             (0, 0): bar_grad(),
             (0, 1): bar_grad(),
@@ -60,7 +60,7 @@ def test_bar_align_left_0points(self):
         }
         assert result == expected
 
-        result = df.style.bar(axis=1)._compute().ctx
+        result = df.style.bar(axis=1, align="left")._compute().ctx
         expected = {
             (0, 0): bar_grad(),
             (0, 1): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),

From debec3e192bae2a38064469e48efe8aee4fb5a1c Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 08:40:52 +0200
Subject: [PATCH 07/11] tests explicit

---
 pandas/tests/io/formats/style/test_align.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/pandas/tests/io/formats/style/test_align.py b/pandas/tests/io/formats/style/test_align.py
index 78fc8051af25c..111e884c279c4 100644
--- a/pandas/tests/io/formats/style/test_align.py
+++ b/pandas/tests/io/formats/style/test_align.py
@@ -21,7 +21,7 @@ def bar_grad(a=None, b=None, c=None, d=None):
 class TestStylerBarAlign:
     def test_bar_align_left(self):
         df = DataFrame({"A": [0, 1, 2]})
-        result = df.style.bar()._compute().ctx
+        result = df.style.bar(align="left")._compute().ctx
         expected = {
             (0, 0): bar_grad(),
             (1, 0): bar_grad(" #d65f5f 50.0%", " transparent 50.0%"),
@@ -29,7 +29,7 @@ def test_bar_align_left(self):
         }
         assert result == expected
 
-        result = df.style.bar(color="red", width=50)._compute().ctx
+        result = df.style.bar(color="red", width=50, align="left")._compute().ctx
         expected = {
             (0, 0): bar_grad(),
             (1, 0): bar_grad(" red 25.0%", " transparent 25.0%"),
@@ -38,10 +38,10 @@ def test_bar_align_left(self):
         assert result == expected
 
         df["C"] = ["a"] * len(df)
-        result = df.style.bar(color="red", width=50)._compute().ctx
+        result = df.style.bar(color="red", width=50, align="left")._compute().ctx
         assert result == expected
         df["C"] = df["C"].astype("category")
-        result = df.style.bar(color="red", width=50)._compute().ctx
+        result = df.style.bar(color="red", width=50, align="left")._compute().ctx
         assert result == expected
 
     def test_bar_align_left_0points(self):
@@ -189,7 +189,7 @@ def test_bar_align_zero_pos_and_neg(self):
 
     def test_bar_align_left_axis_none(self):
         df = DataFrame({"A": [0, 1], "B": [2, 4]})
-        result = df.style.bar(axis=None)._compute().ctx
+        result = df.style.bar(axis=None, align="left")._compute().ctx
         expected = {
             (0, 0): bar_grad(),
             (1, 0): bar_grad(

From 444b0e9469277097a9182df35d1518f63f213750 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 09:11:37 +0200
Subject: [PATCH 08/11] mypy fix and black

---
 pandas/io/formats/style.py | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index 187231942b866..c6eb5119328d7 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2048,7 +2048,7 @@ def bar(
         axis: Axis | None = 0,
         color="#d65f5f",
         width: float = 100,
-        align: str | float | int | callable = "mid",
+        align: str | float | int | Callable = "mid",
         vmin: float | None = None,
         vmax: float | None = None,
         props: str = "width: 10em;",
@@ -2773,7 +2773,7 @@ def _highlight_between(
 
 def _bar(
     data: FrameOrSeries,
-    align: str | float | int | callable,
+    align: str | float | int | Callable,
     colors: list[str],
     width: float,
     vmin: float | None,
@@ -2863,6 +2863,9 @@ def css_calc(x, left: float, right: float, align: str):
         x = left if x < left else x
         x = right if x > right else x  # trim data if outside of the window
 
+        start: float = 0
+        end: float = 1
+
         if align == "left":
             # all proportions are measured from the left side between left and right
             start, end = 0, (x - left) / (right - left)
@@ -2891,44 +2894,41 @@ def css_calc(x, left: float, right: float, align: str):
         elif align == "mid":
             # bars are drawn from zero either leftwards or rightwards with center of
             # cell placed at mid
-            mid = (left + right) / 2
-            if mid < 0:  # get the proportionate location of zero where bars start/end
-                zero_frac = -mid / (right - left) + 0.5
-            else:
-                zero_frac = -left / (right - left)
+            mid: float = (left + right) / 2
+            z_frac: float = (
+                -mid / (right - left) + 0.5 if mid < 0 else -left / (right - left)
+            )
 
             if x < 0:
-                start, end = (x - left) / (right - left), zero_frac
+                start, end = (x - left) / (right - left), z_frac
             else:
-                start, end = zero_frac, (x - left) / (right - left)
+                start, end = z_frac, (x - left) / (right - left)
 
         return css_bar(start * width, end * width, color)
 
     values = data.to_numpy()
     left = np.nanmin(values) if vmin is None else vmin
     right = np.nanmax(values) if vmax is None else vmax
+    z: float = 0  # adjustment to translate data
 
     if align == "mid":
         if np.all(values >= 0):  # "mid" is documented to act as "left" if all positive
-            z, align, left = 0, "left", 0 if vmin is None else vmin
+            align, left = "left", 0 if vmin is None else vmin
         elif np.all(values <= 0):  # "mid" is documented to act as "right" if all neg
-            z, align, right = 0, "right", 0 if vmax is None else vmax
-        else:
-            z = 0
+            align, right = "right", 0 if vmax is None else vmax
     elif align == "mean":
         z, align = np.nanmean(values), "zero"
     elif callable(align):
         z, align = align(values), "zero"
     elif isinstance(align, (float, int)):
         z, align = float(align), "zero"
-    elif align == "left" or align == "right" or align == "zero":
-        z = 0
-    else:
+    elif not (align == "left" or align == "right" or align == "zero"):
         raise ValueError(
             "`align` should be in {'left', 'right', 'mid', 'mean', 'zero'} or be a "
             "value defining the center line or a callable that returns a float"
         )
 
+    assert isinstance(align, str)
     if data.ndim == 1:
         return [css_calc(x - z, left - z, right - z, align) for x in values]
     else:

From e677f067c338f9dbe2e46a8f75d6b342529cd49c Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 14:24:40 +0200
Subject: [PATCH 09/11] add tests for new cases

---
 pandas/io/formats/style.py                  |  2 +-
 pandas/tests/io/formats/style/test_align.py | 78 +++++++++++++++++++++
 2 files changed, 79 insertions(+), 1 deletion(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index c6eb5119328d7..aabafddd23d72 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2102,7 +2102,7 @@ def bar(
             When None (default): the maximum value of the data will be used.
         props : str, optional
             The base CSS of the cell that is extended to add the bar chart. Defaults to
-            `"width: 100px;"`
+            `"width: 10em;"`
 
             .. versionadded:: 1.4.0
 
diff --git a/pandas/tests/io/formats/style/test_align.py b/pandas/tests/io/formats/style/test_align.py
index 111e884c279c4..be7d2fc3be518 100644
--- a/pandas/tests/io/formats/style/test_align.py
+++ b/pandas/tests/io/formats/style/test_align.py
@@ -1,3 +1,4 @@
+import numpy as np
 import pytest
 
 from pandas import DataFrame
@@ -18,6 +19,23 @@ def bar_grad(a=None, b=None, c=None, d=None):
     ]
 
 
+def no_bar():
+    return bar_grad()
+
+
+def bar_to(x):
+    return bar_grad(f" #d65f5f {x:.1f}%", f" transparent {x:.1f}%")
+
+
+def bar_from_to(x, y):
+    return bar_grad(
+        f" transparent {x:.1f}%",
+        f" #d65f5f {x:.1f}%",
+        f" #d65f5f {y:.1f}%",
+        f" transparent {y:.1f}%",
+    )
+
+
 class TestStylerBarAlign:
     def test_bar_align_left(self):
         df = DataFrame({"A": [0, 1, 2]})
@@ -406,3 +424,63 @@ def test_bar_bad_align_raises(self):
         msg = "`align` should be in {'left', 'right', 'mid', 'mean', 'zero'} or"
         with pytest.raises(ValueError, match=msg):
             df.style.bar(align="poorly", color=["#d65f5f", "#5fba7d"]).render()
+
+
+@pytest.mark.parametrize(
+    "align, exp",
+    [
+        ("left", [no_bar(), bar_to(50), bar_to(100)]),
+        ("right", [bar_to(100), bar_from_to(50, 100), no_bar()]),
+        ("mid", [bar_to(33.33), bar_to(66.66), bar_to(100)]),
+        ("zero", [bar_from_to(50, 66.7), bar_from_to(50, 83.3), bar_from_to(50, 100)]),
+        ("mean", [bar_to(50), no_bar(), bar_from_to(50, 100)]),
+        (2.0, [bar_to(50), no_bar(), bar_from_to(50, 100)]),
+        (np.median, [bar_to(50), no_bar(), bar_from_to(50, 100)]),
+    ],
+)
+def test_bar_align_positive_cases(align, exp):
+    # test different align cases for all positive values
+    data = DataFrame([[1], [2], [3]])
+    result = data.style.bar(align=align)._compute().ctx
+    expected = {(0, 0): exp[0], (1, 0): exp[1], (2, 0): exp[2]}
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "align, exp",
+    [
+        ("left", [bar_to(100), bar_to(50), no_bar()]),
+        ("right", [no_bar(), bar_from_to(50, 100), bar_to(100)]),
+        ("mid", [bar_from_to(66.66, 100), bar_from_to(33.33, 100), bar_to(100)]),
+        ("zero", [bar_from_to(33.33, 50), bar_from_to(16.66, 50), bar_to(50)]),
+        ("mean", [bar_from_to(50, 100), no_bar(), bar_to(50)]),
+        (-2.0, [bar_from_to(50, 100), no_bar(), bar_to(50)]),
+        (np.median, [bar_from_to(50, 100), no_bar(), bar_to(50)]),
+    ],
+)
+def test_bar_align_negative_cases(align, exp):
+    # test different align cases for all negative values
+    data = DataFrame([[-1], [-2], [-3]])
+    result = data.style.bar(align=align)._compute().ctx
+    expected = {(0, 0): exp[0], (1, 0): exp[1], (2, 0): exp[2]}
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "align, exp",
+    [
+        ("left", [no_bar(), bar_to(80), bar_to(100)]),
+        ("right", [bar_to(100), bar_from_to(80, 100), no_bar()]),
+        ("mid", [bar_to(60), bar_from_to(60, 80), bar_from_to(60, 100)]),
+        ("zero", [bar_to(50), bar_from_to(50, 66.66), bar_from_to(50, 83.33)]),
+        ("mean", [bar_to(50), bar_from_to(50, 66.66), bar_from_to(50, 83.33)]),
+        (-0.0, [bar_to(50), bar_from_to(50, 66.66), bar_from_to(50, 83.33)]),
+        (np.median, [bar_to(50), no_bar(), bar_from_to(50, 62.5)]),
+    ],
+)
+def test_bar_align_mixed_cases(align, exp):
+    # test different align cases for mixed positive and negative values
+    data = DataFrame([[-3], [1], [2]])
+    result = data.style.bar(align=align)._compute().ctx
+    expected = {(0, 0): exp[0], (1, 0): exp[1], (2, 0): exp[2]}
+    assert result == expected

From 6970a038de525bc99311dccdd1f6f688e04e9250 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Tue, 29 Jun 2021 15:19:19 +0200
Subject: [PATCH 10/11] whats new

---
 doc/source/whatsnew/v1.4.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.4.0.rst b/doc/source/whatsnew/v1.4.0.rst
index 81545ada63ce5..0968ee742185d 100644
--- a/doc/source/whatsnew/v1.4.0.rst
+++ b/doc/source/whatsnew/v1.4.0.rst
@@ -29,7 +29,7 @@ enhancement2
 
 Other enhancements
 ^^^^^^^^^^^^^^^^^^
--
+-  Additional options added to :meth:`.Styler.bar` to control alignment and display (:issue:`26070`)
 -
 
 .. ---------------------------------------------------------------------------

From db18100b8148b5bd3f0b4543ac2df2f8b925d47c Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Wed, 30 Jun 2021 11:50:28 +0200
Subject: [PATCH 11/11] simplify

---
 pandas/io/formats/style.py | 58 ++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 33 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index aabafddd23d72..445e46dbeb767 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -2841,12 +2841,16 @@ def css_calc(x, left: float, right: float, align: str):
         x : float
             Value which determines the bar placement.
         left : float
-            Value marking the left side of calculation.
+            Value marking the left side of calculation, usually minimum of data.
         right : float
-            Value marking the right side of the calculation (left < right).
+            Value marking the right side of the calculation, usually maximum of data
+            (left < right).
         align : {"left", "right", "zero", "mid"}
-            How the bars will be positioned. Note if using "zero" with an adjustment
-            such as a mean, ensure ``left`` and ``right`` are also adjusted on input.
+            How the bars will be positioned.
+            "left", "right", "zero" can be used with any values for ``left``, ``right``.
+            "mid" can only be used where ``left <= 0`` and ``right >= 0``.
+            "zero" is used to specify a center when all values ``x``, ``left``,
+            ``right`` are translated, e.g. by say a mean or median.
 
         Returns
         -------
@@ -2868,36 +2872,24 @@ def css_calc(x, left: float, right: float, align: str):
 
         if align == "left":
             # all proportions are measured from the left side between left and right
-            start, end = 0, (x - left) / (right - left)
+            end = (x - left) / (right - left)
 
         elif align == "right":
             # all proportions are measured from the right side between left and right
-            start, end = (x - left) / (right - left), 1
-
-        elif align == "zero":
-            # all proportions are measured from the center which is set to zero
-            # input data will have been translated if centering about a mean for example
-            if right < 0:
-                right = -left  # since abs(right) < abs(left): all data below zero
-            elif left >= 0:
-                left = -right  # since abs(left) < abs(right): all data above zero
-            elif abs(right) < abs(left):
-                right = -left  # standardise left and right as same distance from zero
-            else:
-                left = -right
+            start = (x - left) / (right - left)
 
-            if x < 0:
-                start, end = (x - left) / (right - left), 0.5
-            else:
-                start, end = 0.5, x / (right - left) + 0.5
-
-        elif align == "mid":
-            # bars are drawn from zero either leftwards or rightwards with center of
-            # cell placed at mid
-            mid: float = (left + right) / 2
-            z_frac: float = (
-                -mid / (right - left) + 0.5 if mid < 0 else -left / (right - left)
-            )
+        else:
+            z_frac: float = 0.5  # location of zero based on the left-right range
+            if align == "zero":
+                # all proportions are measured from the center at zero
+                limit: float = max(abs(left), abs(right))
+                left, right = -limit, limit
+            elif align == "mid":
+                # bars drawn from zero either leftwards or rightwards with center at mid
+                mid: float = (left + right) / 2
+                z_frac = (
+                    -mid / (right - left) + 0.5 if mid < 0 else -left / (right - left)
+                )
 
             if x < 0:
                 start, end = (x - left) / (right - left), z_frac
@@ -2912,9 +2904,9 @@ def css_calc(x, left: float, right: float, align: str):
     z: float = 0  # adjustment to translate data
 
     if align == "mid":
-        if np.all(values >= 0):  # "mid" is documented to act as "left" if all positive
+        if left >= 0:  # "mid" is documented to act as "left" if all values positive
             align, left = "left", 0 if vmin is None else vmin
-        elif np.all(values <= 0):  # "mid" is documented to act as "right" if all neg
+        elif right <= 0:  # "mid" is documented to act as "right" if all values negative
             align, right = "right", 0 if vmax is None else vmax
     elif align == "mean":
         z, align = np.nanmean(values), "zero"
@@ -2928,7 +2920,7 @@ def css_calc(x, left: float, right: float, align: str):
             "value defining the center line or a callable that returns a float"
         )
 
-    assert isinstance(align, str)
+    assert isinstance(align, str)  # mypy: should now be in [left, right, mid, zero]
     if data.ndim == 1:
         return [css_calc(x - z, left - z, right - z, align) for x in values]
     else: