Documentation and naming updates per review (GH 14327)

Author: Jon M. Mease

pandas/indexes/base.py

@@ -432,32 +432,31 @@ def _update_inplace(self, result, **kwargs):
         # guard when called from IndexOpsMixin
         raise TypeError("Index can't be updated inplace")
 
-    def _get_grouper_for_level(self, group_mapper, level):
+    def _get_grouper_for_level(self, mapper, level=None):
         """
         Get index grouper corresponding to an index level
 
         Parameters
         ----------
-        group_mapper: Group mapping function or None
+        mapper: Group mapping function or None
             Function mapping index values to groups
-        level : int
-            Index level (Only used by MultiIndex override)
+        level : int, default None
+            Index level
 
         Returns
         -------
         grouper : Index
             Index of values to group on
         labels : None
             Array of locations in level_index
-            (Only returned by MultiIndex override)
         level_index : None
             Index of unique values for level
-            (Only returned by MultiIndex override)
         """
-        if group_mapper is None:
+        assert level is None or level == 0
+        if mapper is None:
             grouper = self
         else:
-            grouper = self.map(group_mapper)
+            grouper = self.map(mapper)
 
         return grouper, None, None
 

pandas/indexes/multi.py

@@ -539,13 +539,13 @@ def _format_native_types(self, na_rep='nan', **kwargs):
 
         return mi.values
 
-    def _get_grouper_for_level(self, group_mapper, level):
+    def _get_grouper_for_level(self, mapper, level):
         """
         Get index grouper corresponding to an index level
 
         Parameters
         ----------
-        group_mapper: Group mapping function or None
+        mapper: Group mapping function or None
             Function mapping index values to groups
         level : int
             Index level
@@ -556,27 +556,27 @@ def _get_grouper_for_level(self, group_mapper, level):
             Index of values to group on
         labels : ndarray of int or None
             Array of locations in level_index
-        level_index : Index or None
+        uniques : Index or None
             Index of unique values for level
         """
-        inds = self.labels[level]
+        indexer = self.labels[level]
         level_index = self.levels[level]
 
-        if group_mapper is not None:
+        if mapper is not None:
             # Handle group mapping function and return
-            level_values = self.levels[level].take(inds)
-            grouper = level_values.map(group_mapper)
+            level_values = self.levels[level].take(indexer)
+            grouper = level_values.map(mapper)
             return grouper, None, None
 
-        labels, uniques = algos.factorize(inds, sort=True)
+        labels, uniques = algos.factorize(indexer, sort=True)
 
         if len(uniques) > 0 and uniques[0] == -1:
             # Handle NAs
-            mask = inds != -1
-            ok_labels, uniques = algos.factorize(inds[mask],
+            mask = indexer != -1
+            ok_labels, uniques = algos.factorize(indexer[mask],
                                                  sort=True)
 
-            labels = np.empty(len(inds), dtype=inds.dtype)
+            labels = np.empty(len(indexer), dtype=indexer.dtype)
             labels[mask] = ok_labels
             labels[~mask] = -1