BUG: weights is not working for multiple columns in df.plot.hist (#33440)

Author: charlesdong1991

doc/source/whatsnew/v1.1.0.rst

@@ -521,7 +521,7 @@ Plotting
 ^^^^^^^^
 
 - :func:`.plot` for line/bar now accepts color by dictonary (:issue:`8193`).
--
+- Bug in :meth:`DataFrame.plot.hist` where weights are not working for multiple columns (:issue:`33173`)
 - Bug in :meth:`DataFrame.boxplot` and :meth:`DataFrame.plot.boxplot` lost color attributes of ``medianprops``, ``whiskerprops``, ``capprops`` and ``medianprops`` (:issue:`30346`)
 
 

pandas/plotting/_matplotlib/hist.py

@@ -28,10 +28,7 @@ def _args_adjust(self):
             values = values[~isna(values)]
 
             _, self.bins = np.histogram(
-                values,
-                bins=self.bins,
-                range=self.kwds.get("range", None),
-                weights=self.kwds.get("weights", None),
+                values, bins=self.bins, range=self.kwds.get("range", None)
             )
 
         if is_list_like(self.bottom):
@@ -77,6 +74,14 @@ def _make_plot(self):
                 kwds["style"] = style
 
             kwds = self._make_plot_keywords(kwds, y)
+
+            # We allow weights to be a multi-dimensional array, e.g. a (10, 2) array,
+            # and each sub-array (10,) will be called in each iteration. If users only
+            # provide 1D array, we assume the same weights is used for all iterations
+            weights = kwds.get("weights", None)
+            if weights is not None and np.ndim(weights) != 1:
+                kwds["weights"] = weights[:, i]
+
             artists = self._plot(ax, y, column_num=i, stacking_id=stacking_id, **kwds)
             self._add_legend_handle(artists[0], label, index=i)
 

pandas/tests/plotting/test_frame.py

@@ -1682,6 +1682,25 @@ def test_hist_df(self):
         axes = df.plot.hist(rot=50, fontsize=8, orientation="horizontal")
         self._check_ticks_props(axes, xrot=0, yrot=50, ylabelsize=8)
 
+    @pytest.mark.parametrize(
+        "weights", [0.1 * np.ones(shape=(100,)), 0.1 * np.ones(shape=(100, 2))]
+    )
+    def test_hist_weights(self, weights):
+        # GH 33173
+        np.random.seed(0)
+        df = pd.DataFrame(dict(zip(["A", "B"], np.random.randn(2, 100,))))
+
+        ax1 = _check_plot_works(df.plot, kind="hist", weights=weights)
+        ax2 = _check_plot_works(df.plot, kind="hist")
+
+        patch_height_with_weights = [patch.get_height() for patch in ax1.patches]
+
+        # original heights with no weights, and we manually multiply with example
+        # weights, so after multiplication, they should be almost same
+        expected_patch_height = [0.1 * patch.get_height() for patch in ax2.patches]
+
+        tm.assert_almost_equal(patch_height_with_weights, expected_patch_height)
+
     def _check_box_coord(
         self,
         patches,