Fix plotting a DataFrame without 0 in the index

This commit prevents the KeyError raised when DataFrame.plot() is called
with xerr or yerr being a Series or DataFrame whose index doesn't include 0.
The error comes from matplotlib code which tries to access xerr[0] or yerr[0],
so to solve the problem, we convert xerr and yerr from Pandas objects to
NumPy ndarrays before sending them through to matplotlib. This is
a different instance of the same type of problem in Github issues #4493
and #6127 (and perhaps others).

Author: diazona

pandas/tests/test_graphics.py

@@ -3369,6 +3369,33 @@ def _check_errorbar_color(containers, expected, has_err='has_xerr'):
         self._check_has_errorbars(ax, xerr=0, yerr=1)
         _check_errorbar_color(ax.containers, 'green', has_err='has_yerr')
 
+    def test_errorbar_no_zero_in_index(self):
+        a = [1,2,3]
+        s = Series(a, index=a)
+        ax = _check_plot_works(s.plot, yerr=s)
+        self._check_has_errorbars(ax, xerr=0, yerr=1)
+        ax = _check_plot_works(s.plot, xerr=s)
+        self._check_has_errorbars(ax, xerr=1, yerr=0)
+        ax = _check_plot_works(s.plot, xerr=s, yerr=s)
+        self._check_has_errorbars(ax, xerr=1, yerr=1)
+
+        df = DataFrame(a, index=a)
+        ax = _check_plot_works(df.plot, yerr=df)
+        self._check_has_errorbars(ax, xerr=0, yerr=1)
+        ax = _check_plot_works(df.plot, xerr=df)
+        self._check_has_errorbars(ax, xerr=1, yerr=0)
+        ax = _check_plot_works(df.plot, xerr=df, yerr=df)
+        self._check_has_errorbars(ax, xerr=1, yerr=1)
+
+        a = np.array([[4,5,6], [7,8,9]])
+        df = DataFrame(a, index=[1,2], columns=['col1', 'col2', 'col3'])
+        ax = _check_plot_works(df.plot, yerr=df)
+        self._check_has_errorbars(ax, xerr=0, yerr=3)
+        ax = _check_plot_works(df.plot, xerr=df)
+        self._check_has_errorbars(ax, xerr=3, yerr=0)
+        ax = _check_plot_works(df.plot, xerr=df, yerr=df)
+        self._check_has_errorbars(ax, xerr=3, yerr=3)
+
     @slow
     def test_sharex_and_ax(self):
         # https://github.com/pydata/pandas/issues/9737

pandas/tools/plotting.py

@@ -1465,7 +1465,7 @@ def match_labels(data, e):
         return err
 
     def _get_errorbars(self, label=None, index=None, xerr=True, yerr=True):
-        from pandas import DataFrame
+        from pandas import DataFrame, Series
         errors = {}
 
         for kw, flag in zip(['xerr', 'yerr'], [xerr, yerr]):
@@ -1480,7 +1480,9 @@ def _get_errorbars(self, label=None, index=None, xerr=True, yerr=True):
                 elif index is not None and err is not None:
                     err = err[index]
 
-                if err is not None:
+                if isinstance(err, (DataFrame, Series)):
+                    errors[kw] = err.as_matrix()
+                elif err is not None:
                     errors[kw] = err
         return errors