BUG: Inconsistent index for bar plot

Generate the tick position in BarPlot using convert tools from matlab.
Add test for issue pandas-dev#26186
Add test for issue pandas-dev#11465

Author: nrebena

pandas/plotting/_core.py

@@ -1199,7 +1199,6 @@ def __init__(self, data, **kwargs):
         self.bar_width = kwargs.pop('width', 0.5)
         pos = kwargs.pop('position', 0.5)
         kwargs.setdefault('align', 'center')
-        self.tick_pos = np.arange(len(data))
 
         self.bottom = kwargs.pop('bottom', 0)
         self.left = kwargs.pop('left', 0)
@@ -1222,7 +1221,7 @@ def __init__(self, data, **kwargs):
                 self.tickoffset = self.bar_width * pos
                 self.lim_offset = 0
 
-        self.ax_pos = self.tick_pos - self.tickoffset
+        self.ax_index = self.data.index
 
     def _args_adjust(self):
         if is_list_like(self.bottom):
@@ -1249,6 +1248,16 @@ def _make_plot(self):
 
         for i, (label, y) in enumerate(self._iter_data(fillna=0)):
             ax = self._get_ax(i)
+
+            if self.orientation == 'vertical':
+                ax.xaxis.update_units(self.ax_index)
+                self.tick_pos = ax.convert_xunits(self.ax_index)
+                self.ax_pos = self.tick_pos - self.tickoffset
+            elif self.orientation == 'horizontal':
+                ax.yaxis.update_units(self.ax_index)
+                self.tick_pos = ax.convert_yunits(self.ax_index)
+                self.ax_pos = self.tick_pos - self.tickoffset
+
             kwds = self.kwds.copy()
             if self._is_series:
                 kwds['color'] = colors
@@ -1297,9 +1306,8 @@ def _post_plot_logic(self, ax, data):
         else:
             str_index = [pprint_thing(key) for key in range(data.shape[0])]
         name = self._get_index_name()
-
-        s_edge = self.ax_pos[0] - 0.25 + self.lim_offset
-        e_edge = self.ax_pos[-1] + 0.25 + self.bar_width + self.lim_offset
+        s_edge = self.ax_pos.min() - 0.25 + self.lim_offset
+        e_edge = self.ax_pos.max() + 0.25 + self.bar_width + self.lim_offset
 
         self._decorate_ticks(ax, name, str_index, s_edge, e_edge)
 

pandas/tests/plotting/test_frame.py

@@ -1084,14 +1084,17 @@ def test_bar_categorical(self):
         for df in [df1, df2]:
             ax = df.plot.bar()
             ticks = ax.xaxis.get_ticklocs()
-            tm.assert_numpy_array_equal(ticks, np.array([0, 1, 2, 3, 4, 5]))
+            tm.assert_numpy_array_equal(ticks, np.array([0, 1, 2, 3, 4, 5],
+                                                        dtype=np.float))
             assert ax.get_xlim() == (-0.5, 5.5)
             # check left-edge of bars
             assert ax.patches[0].get_x() == -0.25
             assert ax.patches[-1].get_x() == 5.15
 
             ax = df.plot.bar(stacked=True)
-            tm.assert_numpy_array_equal(ticks, np.array([0, 1, 2, 3, 4, 5]))
+            ticks = ax.xaxis.get_ticklocs()
+            tm.assert_numpy_array_equal(ticks, np.array([0, 1, 2, 3, 4, 5],
+                                                        dtype=np.float))
             assert ax.get_xlim() == (-0.5, 5.5)
             assert ax.patches[0].get_x() == -0.25
             assert ax.patches[-1].get_x() == 4.75
@@ -3028,6 +3031,43 @@ def test_x_multiindex_values_ticks(self):
         assert labels_position['(2013, 1)'] == 2.0
         assert labels_position['(2013, 2)'] == 3.0
 
+    @pytest.mark.slow
+    @pytest.mark.parametrize('method', ['bar', 'barh'])
+    def test_bar_ticklabel_consistence(self, method):
+        # Draw two consecutiv bar plot with consistent ticklabels
+        # GH: 26186
+        def get_main_axis(ax):
+            if method == 'barh':
+                return ax.yaxis
+            elif method == 'bar':
+                return ax.xaxis
+        data = {"A": 0, "B": 3, "C": -4}
+        df = pd.DataFrame.from_dict(data, orient="index", columns=["Value"])
+        ax = getattr(df.plot, method)()
+        ax.get_figure().canvas.draw()
+        xticklabels = [t.get_text()
+                       for t in get_main_axis(ax).get_ticklabels()]
+        label_positions_1 = dict(zip(xticklabels,
+                                     get_main_axis(ax).get_ticklocs()))
+        df = df.sort_values("Value") * - 2
+        ax = getattr(df.plot, method)(ax=ax, color="red")
+        ax.get_figure().canvas.draw()
+        xticklabels = [t.get_text()
+                       for t in get_main_axis(ax).get_ticklabels()]
+        label_positions_2 = dict(zip(xticklabels,
+                                     get_main_axis(ax).get_ticklocs()))
+        assert label_positions_1 == label_positions_2
+
+    def test_bar_numeric(self):
+        # Bar plot with numeric index have tick location values equal to index
+        # values
+        # GH: 11465
+        index = np.arange(10, 20)
+        df = pd.DataFrame(np.random.rand(10), index=np.arange(10, 20))
+        ax = df.plot.bar()
+        ticklocs = ax.xaxis.get_ticklocs()
+        tm.assert_numpy_array_equal(ticklocs, index)
+
 
 def _generate_4_axes_via_gridspec():
     import matplotlib.pyplot as plt