BUG: scatter_matrix raising with 2d axis passed (#38668)

Author: mzeitlin11

doc/source/whatsnew/v1.3.0.rst

@@ -262,6 +262,7 @@ Period
 Plotting
 ^^^^^^^^
 
+- Bug in :func:`scatter_matrix` raising when 2d ``ax`` argument passed (:issue:`16253`)
 -
 -
 

pandas/plotting/_matplotlib/tools.py

@@ -196,7 +196,8 @@ def create_subplots(
         fig = plt.figure(**fig_kw)
     else:
         if is_list_like(ax):
-            ax = flatten_axes(ax)
+            if squeeze:
+                ax = flatten_axes(ax)
             if layout is not None:
                 warnings.warn(
                     "When passing multiple axes, layout keyword is ignored", UserWarning
@@ -208,8 +209,8 @@ def create_subplots(
                     UserWarning,
                     stacklevel=4,
                 )
-            if len(ax) == naxes:
-                fig = ax[0].get_figure()
+            if ax.size == naxes:
+                fig = ax.flat[0].get_figure()
                 return fig, ax
             else:
                 raise ValueError(

pandas/tests/plotting/test_misc.py

@@ -94,11 +94,16 @@ def test_bootstrap_plot(self):
 @td.skip_if_no_mpl
 class TestDataFramePlots(TestPlotBase):
     @td.skip_if_no_scipy
-    def test_scatter_matrix_axis(self):
+    @pytest.mark.parametrize("pass_axis", [False, True])
+    def test_scatter_matrix_axis(self, pass_axis):
         from pandas.plotting._matplotlib.compat import mpl_ge_3_0_0
 
         scatter_matrix = plotting.scatter_matrix
 
+        ax = None
+        if pass_axis:
+            _, ax = self.plt.subplots(3, 3)
+
         with tm.RNGContext(42):
             df = DataFrame(np.random.randn(100, 3))
 
@@ -107,7 +112,11 @@ def test_scatter_matrix_axis(self):
             UserWarning, raise_on_extra_warnings=mpl_ge_3_0_0()
         ):
             axes = _check_plot_works(
-                scatter_matrix, filterwarnings="always", frame=df, range_padding=0.1
+                scatter_matrix,
+                filterwarnings="always",
+                frame=df,
+                range_padding=0.1,
+                ax=ax,
             )
         axes0_labels = axes[0][0].yaxis.get_majorticklabels()
 
@@ -121,7 +130,11 @@ def test_scatter_matrix_axis(self):
         # we are plotting multiples on a sub-plot
         with tm.assert_produces_warning(UserWarning):
             axes = _check_plot_works(
-                scatter_matrix, filterwarnings="always", frame=df, range_padding=0.1
+                scatter_matrix,
+                filterwarnings="always",
+                frame=df,
+                range_padding=0.1,
+                ax=ax,
             )
         axes0_labels = axes[0][0].yaxis.get_majorticklabels()
         expected = ["-1.0", "-0.5", "0.0"]