Move feature test to new method, add to whatsnew

Also fix minor bug due to a misnamed var that both the test and pyflakes
missed

Author: stangirala

doc/source/whatsnew/v0.20.0.txt

@@ -366,6 +366,7 @@ Other Enhancements
 - ``pandas.io.json.json_normalize()`` with an empty ``list`` will return an empty ``DataFrame`` (:issue:`15534`)
 - ``pandas.io.json.json_normalize()`` has gained a ``sep`` option that accepts ``str`` to separate joined fields; the default is ".", which is backward compatible. (:issue:`14883`)
 - ``pd.read_csv()`` will now raise a ``csv.Error`` error whenever an end-of-file character is encountered in the middle of a data row (:issue:`15913`)
+- ``parallel_coordinates()`` now has a ``sort_labels`` keyword arg that sorts class labels and the colours assigned to them (:issue:`15908`)
 
 
 .. _ISO 8601 duration: https://en.wikipedia.org/wiki/ISO_8601#Durations

pandas/tests/plotting/test_misc.py

@@ -241,12 +241,16 @@ def test_parallel_coordinates(self):
         with tm.assert_produces_warning(FutureWarning):
             parallel_coordinates(df, 'Name', colors=colors)
 
+    def test_parallel_coordinates_with_sorted_labels(self):
+        """ For #15908 """
+        from pandas.tools.plotting import parallel_coordinates
+
         df = DataFrame({"feat": [i for i in range(30)],
                         "class": [2 for _ in range(10)] +
                         [3 for _ in range(10)] +
                         [1 for _ in range(10)]})
         ax = parallel_coordinates(df, 'class', sort_labels=True)
-        polylines, lables = ax.get_legend_handles_labels()
+        polylines, labels = ax.get_legend_handles_labels()
         color_label_tuples = \
             zip([polyline.get_color() for polyline in polylines], labels)
         ordered_color_label_tuples = sorted(color_label_tuples,

pandas/tools/plotting.py

@@ -719,8 +719,11 @@ def parallel_coordinates(frame, class_column, cols=None, ax=None, color=None,
         If true, vertical lines will be added at each xtick
     axvlines_kwds: keywords, optional
         Options to be passed to axvline method for vertical lines
-    sort_labels: bool, optional
+    sort_labels: bool, False
         Sort class_column labels, useful when assigning colours
+
+        .. versionadded:: 0.20.0
+
     kwds: keywords
         Options to pass to matplotlib plotting method
 
@@ -779,6 +782,7 @@ def parallel_coordinates(frame, class_column, cols=None, ax=None, color=None,
 
     if sort_labels is True:
         classes = sorted(classes)
+        color_values = sorted(color_values)
     colors = dict(zip(classes, color_values))
 
     for i in range(n):