API: support c and colormap args for DataFrame.plot with kind='scatter'

doc/source/v0.15.0.txt

@@ -435,6 +435,8 @@ Enhancements
 
 - Added ``layout`` keyword to ``DataFrame.plot`` (:issue:`6667`)
 - Allow to pass multiple axes to ``DataFrame.plot``, ``hist`` and ``boxplot`` (:issue:`5353`, :issue:`6970`, :issue:`7069`)
+- Added support for ``c``, ``colormap`` and ``colorbar`` arguments for
+  ``DataFrame.plot`` with ``kind='scatter'`` (:issue:`7780`)
 
 
 - ``PeriodIndex`` supports ``resolution`` as the same as ``DatetimeIndex`` (:issue:`7708`)

doc/source/visualization.rst

@@ -521,6 +521,14 @@ It is recommended to specify ``color`` and ``label`` keywords to distinguish eac
    df.plot(kind='scatter', x='c', y='d',
            color='DarkGreen', label='Group 2', ax=ax);
 
+The keyword ``c`` may be given as the name of a column to provide colors for
+each point:
+
+.. ipython:: python
+
+   @savefig scatter_plot_colored.png
+   df.plot(kind='scatter', x='a', y='b', c='c', s=50);
+
 You can pass other keywords supported by matplotlib ``scatter``.
 Below example shows a bubble chart using a dataframe column values as bubble size.
 

pandas/tests/test_graphics.py

@@ -1497,6 +1497,34 @@ def test_plot_scatter(self):
         axes = df.plot(x='x', y='y', kind='scatter', subplots=True)
         self._check_axes_shape(axes, axes_num=1, layout=(1, 1))
 
+    @slow
+    def test_plot_scatter_with_c(self):
+        df = DataFrame(randn(6, 4),
+                       index=list(string.ascii_letters[:6]),
+                       columns=['x', 'y', 'z', 'four'])
+
+        axes = [df.plot(kind='scatter', x='x', y='y', c='z'),
+                df.plot(kind='scatter', x=0, y=1, c=2)]
+        for ax in axes:
+            # default to RdBu
+            self.assertEqual(ax.collections[0].cmap.name, 'RdBu')
+            # n.b. there appears to be no public method to get the colorbar
+            # label
+            self.assertEqual(ax.collections[0].colorbar._label, 'z')
+
+        cm = 'cubehelix'
+        ax = df.plot(kind='scatter', x='x', y='y', c='z', colormap=cm)
+        self.assertEqual(ax.collections[0].cmap.name, cm)
+
+        # verify turning off colorbar works
+        ax = df.plot(kind='scatter', x='x', y='y', c='z', colorbar=False)
+        self.assertIs(ax.collections[0].colorbar, None)
+
+        # verify that we can still plot a solid color
+        ax = df.plot(x=0, y=1, c='red', kind='scatter')
+        self.assertIs(ax.collections[0].colorbar, None)
+        self._check_colors(ax.collections, facecolors=['r'])
+
     @slow
     def test_plot_bar(self):
         df = DataFrame(randn(6, 4),

pandas/tools/plotting.py

@@ -1368,32 +1368,55 @@ def _get_errorbars(self, label=None, index=None, xerr=True, yerr=True):
 class ScatterPlot(MPLPlot):
     _layout_type = 'single'
 
-    def __init__(self, data, x, y, **kwargs):
+    def __init__(self, data, x, y, c=None, **kwargs):
         MPLPlot.__init__(self, data, **kwargs)
-        self.kwds.setdefault('c', self.plt.rcParams['patch.facecolor'])
         if x is None or y is None:
             raise ValueError( 'scatter requires and x and y column')
         if com.is_integer(x) and not self.data.columns.holds_integer():
             x = self.data.columns[x]
         if com.is_integer(y) and not self.data.columns.holds_integer():
             y = self.data.columns[y]
+        if com.is_integer(c) and not self.data.columns.holds_integer():
+            c = self.data.columns[c]
         self.x = x
         self.y = y
+        self.c = c
 
     @property
     def nseries(self):
         return 1
 
     def _make_plot(self):
-        x, y, data = self.x, self.y, self.data
+        import matplotlib.pyplot as plt
+
+        x, y, c, data = self.x, self.y, self.c, self.data
         ax = self.axes[0]
 
+        # plot a colorbar only if a colormap is provided or necessary
+        cb = self.kwds.pop('colorbar', self.colormap or c in self.data.columns)
+
+        # pandas uses colormap, matplotlib uses cmap.
+        cmap = self.colormap or 'RdBu'
+        cmap = plt.cm.get_cmap(cmap)
+
+        if c is None:
+            c_values = self.plt.rcParams['patch.facecolor']
+        elif c in self.data.columns:
+            c_values = self.data[c].values
+        else:
+            c_values = c
+
         if self.legend and hasattr(self, 'label'):
             label = self.label
         else:
             label = None
-        scatter = ax.scatter(data[x].values, data[y].values, label=label,
-                             **self.kwds)
+        scatter = ax.scatter(data[x].values, data[y].values, c=c_values,
+                             label=label, cmap=cmap, **self.kwds)
+        if cb:
+            img = ax.collections[0]
+            cb_label = c if c in self.data.columns else ''
+            self.fig.colorbar(img, ax=ax, label=cb_label)
+
         self._add_legend_handle(scatter, label)
 
         errors_x = self._get_errorbars(label=x, index=0, yerr=False)
@@ -2259,6 +2282,8 @@ def plot_frame(frame=None, x=None, y=None, subplots=False, sharex=True,
     colormap : str or matplotlib colormap object, default None
         Colormap to select colors from. If string, load colormap with that name
         from matplotlib.
+    colorbar : boolean, optional
+        If True, plot colorbar (only relevant for 'scatter' and 'hexbin' plots)
     position : float
         Specify relative alignments for bar plot layout.
         From 0 (left/bottom-end) to 1 (right/top-end). Default is 0.5 (center)
@@ -2285,6 +2310,9 @@ def plot_frame(frame=None, x=None, y=None, subplots=False, sharex=True,
     `C` specifies the value at each `(x, y)` point and `reduce_C_function`
     is a function of one argument that reduces all the values in a bin to
     a single number (e.g. `mean`, `max`, `sum`, `std`).
+
+    If `kind`='scatter' and the argument `c` is the name of a dataframe column,
+    the values of that column are used to color each point.
     """
 
     kind = _get_standard_kind(kind.lower().strip())