From 8309f1330fa8925c891863cfb61116fed2d1f64d Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Sat, 6 Mar 2021 17:10:36 -0800
Subject: [PATCH 1/2] REF: Block.putmask dont use split_and_operate

---
 pandas/core/array_algos/putmask.py |  2 +-
 pandas/core/internals/blocks.py    | 61 +++++++++++-------------------
 2 files changed, 24 insertions(+), 39 deletions(-)

diff --git a/pandas/core/array_algos/putmask.py b/pandas/core/array_algos/putmask.py
index cfa1f59f3d4ca..93046f476c6ba 100644
--- a/pandas/core/array_algos/putmask.py
+++ b/pandas/core/array_algos/putmask.py
@@ -81,7 +81,7 @@ def putmask_smart(values: np.ndarray, mask: np.ndarray, new) -> np.ndarray:
 
     # n should be the length of the mask or a scalar here
     if not is_list_like(new):
-        new = np.repeat(new, len(mask))
+        new = np.broadcast_to(new, mask.shape)
 
     # see if we are only masking values that if putted
     # will work in the current dtype
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index f2b8499a316b7..458c923ac46eb 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -1061,21 +1061,17 @@ def putmask(self, mask, new) -> List[Block]:
         -------
         List[Block]
         """
-        transpose = self.ndim == 2
+        orig_mask = mask
         mask, noop = validate_putmask(self.values.T, mask)
         assert not isinstance(new, (ABCIndex, ABCSeries, ABCDataFrame))
 
-        new_values = self.values  # delay copy if possible.
         # if we are passed a scalar None, convert it here
-        if not is_list_like(new) and isna(new) and not self.is_object:
-            # FIXME: make sure we have compatible NA
+        if not self.is_object and is_valid_na_for_dtype(new, self.dtype):
             new = self.fill_value
 
         if self._can_hold_element(new):
-            if transpose:
-                new_values = new_values.T
 
-            putmask_without_repeat(new_values, mask, new)
+            putmask_without_repeat(self.values.T, mask, new)
             return [self]
 
         elif noop:
@@ -1083,42 +1079,31 @@ def putmask(self, mask, new) -> List[Block]:
 
         dtype, _ = infer_dtype_from(new)
         if dtype.kind in ["m", "M"]:
-            # using putmask with object dtype will incorrect cast to object
+            # using putmask with object dtype will incorrectly cast to object
             # Having excluded self._can_hold_element, we know we cannot operate
             #  in-place, so we are safe using `where`
             return self.where(new, ~mask)
 
-        else:
-            # may need to upcast
-            if transpose:
-                mask = mask.T
-                if isinstance(new, np.ndarray):
-                    new = new.T
-
-            # operate column-by-column
-            def f(mask, val, idx):
-
-                if idx is None:
-                    # ndim==1 case.
-                    n = new
-                else:
-
-                    if isinstance(new, np.ndarray):
-                        n = np.squeeze(new[idx % new.shape[0]])
-                    else:
-                        n = np.array(new)
-
-                    # type of the new block
-                    dtype = find_common_type([n.dtype, val.dtype])
-
-                    # we need to explicitly astype here to make a copy
-                    n = n.astype(dtype)
-
-                nv = putmask_smart(val, mask, n)
-                return nv
+        elif self.ndim == 1 or self.shape[0] == 1:
+            # no need to split columns
+            nv = putmask_smart(self.values.T, mask, new).T
+            return [self.make_block(nv)]
 
-            new_blocks = self.split_and_operate(mask, f, True)
-            return new_blocks
+        else:
+            is_array = isinstance(new, np.ndarray)
+
+            res_blocks = []
+            nbs = self._split()
+            for i, nb in enumerate(nbs):
+                n = new
+                if is_array:
+                    # we have a different value per-column
+                    n = new.T[[i]].T
+
+                submask = orig_mask.T[[i]].T
+                rbs = nb.putmask(submask, n)
+                res_blocks.extend(rbs)
+            return res_blocks
 
     @final
     def coerce_to_target_dtype(self, other) -> Block:

From 18d304f6adcf7054ee1169de0e2202e09f235b38 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Sat, 6 Mar 2021 17:31:41 -0800
Subject: [PATCH 2/2] simplify

---
 pandas/core/internals/blocks.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 458c923ac46eb..e0af81d22c940 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -1098,9 +1098,9 @@ def putmask(self, mask, new) -> List[Block]:
                 n = new
                 if is_array:
                     # we have a different value per-column
-                    n = new.T[[i]].T
+                    n = new[:, i : i + 1]
 
-                submask = orig_mask.T[[i]].T
+                submask = orig_mask[:, i : i + 1]
                 rbs = nb.putmask(submask, n)
                 res_blocks.extend(rbs)
             return res_blocks