Merge pull request #13026 from jklymak/mnt-add-warning-for-categorical

dstansby · web-flow · commit df10f3e389d2 · 2019-01-20T12:05:51.000Z
MNT: add a logging call if a categorical string array is all convertible
diff --git a/lib/matplotlib/category.py b/lib/matplotlib/category.py
@@ -12,14 +12,20 @@
 """
 
 from collections import OrderedDict
+import dateutil.parser
 import itertools
+import logging
 
 import numpy as np
 
+import matplotlib.cbook as cbook
 import matplotlib.units as units
 import matplotlib.ticker as ticker
 
 
+_log = logging.getLogger(__name__)
+
+
 class StrCategoryConverter(units.ConversionInterface):
     @staticmethod
     def convert(value, unit, axis):
@@ -174,6 +180,21 @@ def __init__(self, data=None):
         if data is not None:
             self.update(data)
 
+    @staticmethod
+    def _str_is_convertible(val):
+        """
+        Helper method to see if a string can be cast to float or
+        parsed as date.
+        """
+        try:
+            float(val)
+        except ValueError:
+            try:
+                dateutil.parser.parse(val)
+            except ValueError:
+                return False
+        return True
+
     def update(self, data):
         """Maps new values to integer identifiers.
 
@@ -189,11 +210,22 @@ def update(self, data):
         """
         data = np.atleast_1d(np.array(data, dtype=object))
 
+        # check if convertable to number:
+        convertable = True
         for val in OrderedDict.fromkeys(data):
+            # OrderedDict just iterates over unique values in data.
             if not isinstance(val, (str, bytes)):
                 raise TypeError("{val!r} is not a string".format(val=val))
+            if convertable:
+                # this will only be called so long as convertable is True.
+                convertable = self._str_is_convertible(val)
             if val not in self._mapping:
                 self._mapping[val] = next(self._counter)
+        if convertable:
+            _log.info('Using categorical units to plot a list of strings '
+                      'that are all parsable as floats or dates. If these '
+                      'strings should be plotted as numbers, cast to the '
+                      'approriate data type before plotting.')
 
 
 # Register the converter with Matplotlib's unit framework
