add violin orientation param

doc/api/next_api_changes/deprecations/27998-TS.rst

@@ -0,0 +1,7 @@
+``violinplot`` and ``violin`` *vert* parameter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The parameter *vert: bool* has been deprecated on `~.Axes.violinplot` and
+`~.Axes.violin`.
+It will be replaced by *orientation: {"vertical", "horizontal"}* for API
+consistency.

doc/users/next_whats_new/violinplot_orientation.rst

@@ -0,0 +1,21 @@
+``violinplot`` and ``violin`` orientation parameter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Violinplots have a new parameter *orientation: {"vertical", "horizontal"}*
+to change the orientation of the plot. This will replace the deprecated
+*vert: bool* parameter.
+
+
+.. plot::
+    :include-source: true
+    :alt: Example of creating 4 horizontal violinplots.
+
+    import matplotlib.pyplot as plt
+    import numpy as np
+
+    fig, ax = plt.subplots()
+    np.random.seed(19680801)
+    all_data = [np.random.normal(0, std, 100) for std in range(6, 10)]
+
+    ax.violinplot(all_data, orientation='horizontal')
+    plt.show()

galleries/examples/statistics/violinplot.py

@@ -62,37 +62,37 @@
                      quantiles=[0.05, 0.1, 0.8, 0.9], bw_method=0.5, side='high')
 axs[0, 5].set_title('Custom violin 6', fontsize=fs)
 
-axs[1, 0].violinplot(data, pos, points=80, vert=False, widths=0.7,
+axs[1, 0].violinplot(data, pos, points=80, orientation='horizontal', widths=0.7,
                      showmeans=True, showextrema=True, showmedians=True)
 axs[1, 0].set_title('Custom violin 7', fontsize=fs)
 
-axs[1, 1].violinplot(data, pos, points=100, vert=False, widths=0.9,
+axs[1, 1].violinplot(data, pos, points=100, orientation='horizontal', widths=0.9,
                      showmeans=True, showextrema=True, showmedians=True,
                      bw_method='silverman')
 axs[1, 1].set_title('Custom violin 8', fontsize=fs)
 
-axs[1, 2].violinplot(data, pos, points=200, vert=False, widths=1.1,
+axs[1, 2].violinplot(data, pos, points=200, orientation='horizontal', widths=1.1,
                      showmeans=True, showextrema=True, showmedians=True,
                      bw_method=0.5)
 axs[1, 2].set_title('Custom violin 9', fontsize=fs)
 
-axs[1, 3].violinplot(data, pos, points=200, vert=False, widths=1.1,
+axs[1, 3].violinplot(data, pos, points=200, orientation='horizontal', widths=1.1,
                      showmeans=True, showextrema=True, showmedians=True,
                      quantiles=[[0.1], [], [], [0.175, 0.954], [0.75], [0.25]],
                      bw_method=0.5)
 axs[1, 3].set_title('Custom violin 10', fontsize=fs)
 
-axs[1, 4].violinplot(data[-1:], pos[-1:], points=200, vert=False, widths=1.1,
-                     showmeans=True, showextrema=True, showmedians=True,
+axs[1, 4].violinplot(data[-1:], pos[-1:], points=200, orientation='horizontal',
+                     widths=1.1, showmeans=True, showextrema=True, showmedians=True,
                      quantiles=[0.05, 0.1, 0.8, 0.9], bw_method=0.5)
 axs[1, 4].set_title('Custom violin 11', fontsize=fs)
 
-axs[1, 5].violinplot(data[-1:], pos[-1:], points=200, vert=False, widths=1.1,
-                     showmeans=True, showextrema=True, showmedians=True,
+axs[1, 5].violinplot(data[-1:], pos[-1:], points=200, orientation='horizontal',
+                     widths=1.1, showmeans=True, showextrema=True, showmedians=True,
                      quantiles=[0.05, 0.1, 0.8, 0.9], bw_method=0.5, side='low')
 
-axs[1, 5].violinplot(data[-1:], pos[-1:], points=200, vert=False, widths=1.1,
-                     showmeans=True, showextrema=True, showmedians=True,
+axs[1, 5].violinplot(data[-1:], pos[-1:], points=200, orientation='horizontal',
+                     widths=1.1, showmeans=True, showextrema=True, showmedians=True,
                      quantiles=[0.05, 0.1, 0.8, 0.9], bw_method=0.5, side='high')
 axs[1, 5].set_title('Custom violin 12', fontsize=fs)
 

lib/matplotlib/axes/_axes.py

@@ -8350,9 +8350,10 @@ def matshow(self, Z, **kwargs):
 
     @_api.make_keyword_only("3.9", "vert")
     @_preprocess_data(replace_names=["dataset"])
-    def violinplot(self, dataset, positions=None, vert=True, widths=0.5,
+    def violinplot(self, dataset, positions=None, vert=None, widths=0.5,
                    showmeans=False, showextrema=True, showmedians=False,
-                   quantiles=None, points=100, bw_method=None, side='both'):
+                   quantiles=None, points=100, bw_method=None, side='both',
+                   orientation=None):
         """
         Make a violin plot.
 
@@ -8371,8 +8372,14 @@ def violinplot(self, dataset, positions=None, vert=True, widths=0.5,
             vertical violins (or y-axis for horizontal violins).
 
         vert : bool, default: True.
-            If true, creates a vertical violin plot.
-            Otherwise, creates a horizontal violin plot.
+            .. deprecated:: 3.10
+                Use *orientation* instead.
+
+                If this is given during the deprecation period, it overrides
+                the *orientation* parameter.
+
+            If True, plots the violins vertically.
+            If False, plots the violins horizontally.
 
         widths : float or array-like, default: 0.5
             The maximum width of each violin in units of the *positions* axis.
@@ -8407,6 +8414,12 @@ def violinplot(self, dataset, positions=None, vert=True, widths=0.5,
             'both' plots standard violins. 'low'/'high' only
             plots the side below/above the positions value.
 
+        orientation : {'vertical', 'horizontal'}, default: 'vertical'
+            If 'horizontal', plots the violins horizontally.
+            Otherwise, plots the violins vertically.
+
+            .. versionadded:: 3.10
+
         data : indexable object, optional
             DATA_PARAMETER_PLACEHOLDER
 
@@ -8457,12 +8470,14 @@ def _kde_method(X, coords):
         vpstats = cbook.violin_stats(dataset, _kde_method, points=points,
                                      quantiles=quantiles)
         return self.violin(vpstats, positions=positions, vert=vert,
-                           widths=widths, showmeans=showmeans,
-                           showextrema=showextrema, showmedians=showmedians, side=side)
+                           orientation=orientation, widths=widths,
+                           showmeans=showmeans, showextrema=showextrema,
+                           showmedians=showmedians, side=side)
 
     @_api.make_keyword_only("3.9", "vert")
-    def violin(self, vpstats, positions=None, vert=True, widths=0.5,
-               showmeans=False, showextrema=True, showmedians=False, side='both'):
+    def violin(self, vpstats, positions=None, vert=None, widths=0.5,
+               showmeans=False, showextrema=True, showmedians=False, side='both',
+               orientation=None):
         """
         Draw a violin plot from pre-computed statistics.
 
@@ -8501,8 +8516,14 @@ def violin(self, vpstats, positions=None, vert=True, widths=0.5,
             vertical violins (or y-axis for horizontal violins).
 
         vert : bool, default: True.
-            If true, plots the violins vertically.
-            Otherwise, plots the violins horizontally.
+            .. deprecated:: 3.10
+                Use *orientation* instead.
+
+                If this is given during the deprecation period, it overrides
+                the *orientation* parameter.
+
+            If True, plots the violins vertically.
+            If False, plots the violins horizontally.
 
         widths : float or array-like, default: 0.5
             The maximum width of each violin in units of the *positions* axis.
@@ -8522,6 +8543,12 @@ def violin(self, vpstats, positions=None, vert=True, widths=0.5,
             'both' plots standard violins. 'low'/'high' only
             plots the side below/above the positions value.
 
+        orientation : {'vertical', 'horizontal'}, default: 'vertical'
+            If 'horizontal', plots the violins horizontally.
+            Otherwise, plots the violins vertically.
+
+            .. versionadded:: 3.10
+
         Returns
         -------
         dict
@@ -8572,6 +8599,24 @@ def violin(self, vpstats, positions=None, vert=True, widths=0.5,
         datashape_message = ("List of violinplot statistics and `{0}` "
                              "values must have the same length")
 
+        if vert is not None:
+            _api.warn_deprecated(
+                "3.10",
+                name="vert: bool",
+                alternative="orientation: {'vertical', 'horizontal'}"
+            )
+
+        # vert and orientation parameters are linked until vert's
+        # deprecation period expires. If both are selected,
+        # vert takes precedence.
+        if vert or vert is None and orientation is None:
+            orientation = 'vertical'
+        elif vert is False:
+            orientation = 'horizontal'
+
+        if orientation is not None:
+            _api.check_in_list(['horizontal', 'vertical'], orientation=orientation)
+
         # Validate positions
         if positions is None:
             positions = range(1, N + 1)
@@ -8600,7 +8645,7 @@ def violin(self, vpstats, positions=None, vert=True, widths=0.5,
             fillcolor = linecolor = self._get_lines.get_next_color()
 
         # Check whether we are rendering vertically or horizontally
-        if vert:
+        if orientation == 'vertical':
             fill = self.fill_betweenx
             if side in ['low', 'high']:
                 perp_lines = functools.partial(self.hlines, colors=linecolor,

lib/matplotlib/axes/_axes.pyi

@@ -739,7 +739,7 @@ class Axes(_AxesBase):
         dataset: ArrayLike | Sequence[ArrayLike],
         positions: ArrayLike | None = ...,
         *,
-        vert: bool = ...,
+        vert: bool | None = ...,
         widths: float | ArrayLike = ...,
         showmeans: bool = ...,
         showextrema: bool = ...,
@@ -751,19 +751,21 @@ class Axes(_AxesBase):
         | Callable[[GaussianKDE], float]
         | None = ...,
         side: Literal["both", "low", "high"] = ...,
+        orientation: Literal["vertical", "horizontal"] | None = ...,
         data=...,
     ) -> dict[str, Collection]: ...
     def violin(
         self,
         vpstats: Sequence[dict[str, Any]],
         positions: ArrayLike | None = ...,
         *,
-        vert: bool = ...,
+        vert: bool | None = ...,
         widths: float | ArrayLike = ...,
         showmeans: bool = ...,
         showextrema: bool = ...,
         showmedians: bool = ...,
         side: Literal["both", "low", "high"] = ...,
+        orientation: Literal["vertical", "horizontal"] | None = ...,
     ) -> dict[str, Collection]: ...
 
     table = mtable.table

lib/matplotlib/pyplot.py

@@ -4142,7 +4142,7 @@ def triplot(*args, **kwargs):
 def violinplot(
     dataset: ArrayLike | Sequence[ArrayLike],
     positions: ArrayLike | None = None,
-    vert: bool = True,
+    vert: bool | None = None,
     widths: float | ArrayLike = 0.5,
     showmeans: bool = False,
     showextrema: bool = True,
@@ -4154,6 +4154,7 @@ def violinplot(
     | Callable[[GaussianKDE], float]
     | None = None,
     side: Literal["both", "low", "high"] = "both",
+    orientation: Literal["vertical", "horizontal"] | None = None,
     *,
     data=None,
 ) -> dict[str, Collection]:
@@ -4169,6 +4170,7 @@ def violinplot(
         points=points,
         bw_method=bw_method,
         side=side,
+        orientation=orientation,
         **({"data": data} if data is not None else {}),
     )
 

lib/matplotlib/tests/test_axes.py

@@ -9034,3 +9034,40 @@ def test_latex_pie_percent(fig_test, fig_ref):
 
     ax1 = fig_ref.subplots()
     ax1.pie(data, autopct=r"%1.0f\%%", textprops={'usetex': True})
+
+
+@check_figures_equal(extensions=['png'])
+def test_violinplot_orientation(fig_test, fig_ref):
+    # Test the `orientation : {'vertical', 'horizontal'}`
+    # parameter and deprecation of `vert: bool`.
+    fig, axs = plt.subplots(nrows=1, ncols=3)
+    np.random.seed(19680801)
+    all_data = [np.random.normal(0, std, 100) for std in range(6, 10)]
+
+    axs[0].violinplot(all_data)  # Default vertical plot.
+    # xticks and yticks should be at their default position.
+    assert all(axs[0].get_xticks() == np.array(
+        [0.5, 1., 1.5, 2., 2.5, 3., 3.5, 4., 4.5]))
+    assert all(axs[0].get_yticks() == np.array(
+        [-30., -20., -10., 0., 10., 20., 30.]))
+
+    # Horizontal plot using new `orientation` keyword.
+    axs[1].violinplot(all_data, orientation='horizontal')
+    # xticks and yticks should be swapped.
+    assert all(axs[1].get_xticks() == np.array(
+        [-30., -20., -10., 0., 10., 20., 30.]))
+    assert all(axs[1].get_yticks() == np.array(
+        [0.5, 1., 1.5, 2., 2.5, 3., 3.5, 4., 4.5]))
+
+    plt.close()
+
+    # Deprecation of `vert: bool` keyword
+    with pytest.warns(mpl.MatplotlibDeprecationWarning,
+                      match='vert: bool was deprecated in Matplotlib 3.10'):
+        # Compare images between a figure that
+        # uses vert and one that uses orientation.
+        ax_ref = fig_ref.subplots()
+        ax_ref.violinplot(all_data, vert=False)
+
+        ax_test = fig_test.subplots()
+        ax_test.violinplot(all_data, orientation='horizontal')