BUG: Plotting use FixedLocator (#26185)

closes #7612
closes #15912
closes #22334

Author: nrebena

doc/source/whatsnew/v0.25.0.rst

@@ -374,7 +374,7 @@ Plotting
 
 - Fixed bug where :class:`api.extensions.ExtensionArray` could not be used in matplotlib plotting (:issue:`25587`)
 - Bug in an error message in :meth:`DataFrame.plot`. Improved the error message if non-numerics are passed to :meth:`DataFrame.plot` (:issue:`25481`)
--
+- Bug in incorrect ticklabel positions when plotting an index that are non-numeric / non-datetime (:issue:`7612` :issue:`15912` :issue:`22334`)
 -
 -
 

pandas/plotting/_core.py

@@ -401,6 +401,7 @@ def _add_table(self):
 
     def _post_plot_logic_common(self, ax, data):
         """Common post process for each axes"""
+        from matplotlib.ticker import FixedLocator, FixedFormatter
 
         def get_label(i):
             try:
@@ -410,8 +411,12 @@ def get_label(i):
 
         if self.orientation == 'vertical' or self.orientation is None:
             if self._need_to_set_index:
-                xticklabels = [get_label(x) for x in ax.get_xticks()]
+                xticks = ax.get_xticks()
+                xticklabels = [get_label(x) for x in xticks]
                 ax.set_xticklabels(xticklabels)
+                ax.xaxis.set_major_locator(FixedLocator(xticks))
+                ax.xaxis.set_major_formatter(FixedFormatter(xticklabels))
+
             self._apply_axis_properties(ax.xaxis, rot=self.rot,
                                         fontsize=self.fontsize)
             self._apply_axis_properties(ax.yaxis, fontsize=self.fontsize)
@@ -422,8 +427,11 @@ def get_label(i):
 
         elif self.orientation == 'horizontal':
             if self._need_to_set_index:
-                yticklabels = [get_label(y) for y in ax.get_yticks()]
+                yticks = ax.get_yticks()
+                yticklabels = [get_label(y) for y in yticks]
                 ax.set_yticklabels(yticklabels)
+                ax.xaxis.set_major_locator(FixedLocator(yticks))
+                ax.xaxis.set_major_formatter(FixedFormatter(yticklabels))
             self._apply_axis_properties(ax.yaxis, rot=self.rot,
                                         fontsize=self.fontsize)
             self._apply_axis_properties(ax.xaxis, fontsize=self.fontsize)

pandas/tests/plotting/test_frame.py

@@ -2995,6 +2995,40 @@ def test_secondary_axis_font_size(self, method):
         self._check_ticks_props(axes=ax.right_ax,
                                 ylabelsize=fontsize)
 
+    @pytest.mark.slow
+    def test_x_string_values_ticks(self):
+        # Test if string plot index have a fixed xtick position
+        # GH: 7612, GH: 22334
+        df = pd.DataFrame({'sales': [3, 2, 3],
+                           'visits': [20, 42, 28],
+                           'day': ['Monday', 'Tuesday', 'Wednesday']})
+        ax = df.plot.area(x='day')
+        ax.set_xlim(-1, 3)
+        xticklabels = [t.get_text() for t in ax.get_xticklabels()]
+        labels_position = dict(zip(xticklabels, ax.get_xticks()))
+        # Testing if the label stayed at the right position
+        assert labels_position['Monday'] == 0.0
+        assert labels_position['Tuesday'] == 1.0
+        assert labels_position['Wednesday'] == 2.0
+
+    @pytest.mark.slow
+    def test_x_multiindex_values_ticks(self):
+        # Test if multiindex plot index have a fixed xtick position
+        # GH: 15912
+        index = pd.MultiIndex.from_product([[2012, 2013], [1, 2]])
+        df = pd.DataFrame(np.random.randn(4, 2),
+                          columns=['A', 'B'],
+                          index=index)
+        ax = df.plot()
+        ax.set_xlim(-1, 4)
+        xticklabels = [t.get_text() for t in ax.get_xticklabels()]
+        labels_position = dict(zip(xticklabels, ax.get_xticks()))
+        # Testing if the label stayed at the right position
+        assert labels_position['(2012, 1)'] == 0.0
+        assert labels_position['(2012, 2)'] == 1.0
+        assert labels_position['(2013, 1)'] == 2.0
+        assert labels_position['(2013, 2)'] == 3.0
+
 
 def _generate_4_axes_via_gridspec():
     import matplotlib.pyplot as plt