Various changes

Author: topper-123

pandas/core/groupby/generic.py

@@ -654,7 +654,8 @@ def value_counts(
         rep = partial(np.repeat, repeats=np.add.reduceat(inc, idx))
 
         # multi-index components
-        codes = list(map(rep, self.grouper.recons_codes)) + [llab(lab, inc)]
+        codes = self.grouper.recons_codes
+        codes = [rep(level_codes) for level_codes in codes] + [llab(lab, inc)]
         levels = [ping.group_index for ping in self.grouper.groupings] + [lev]
         names = self.grouper.names + [self._selection_name]
 
@@ -693,8 +694,8 @@ def value_counts(
         # for compat. with libgroupby.value_counts need to ensure every
         # bin is present at every index level, null filled with zeros
         diff = np.zeros(len(out), dtype="bool")
-        for codes_ in codes[:-1]:
-            diff |= np.r_[True, codes_[1:] != codes_[:-1]]
+        for level_codes in codes[:-1]:
+            diff |= np.r_[True, level_codes[1:] != level_codes[:-1]]
 
         ncat, nbin = diff.sum(), len(levels[-1])
 
@@ -710,7 +711,10 @@ def value_counts(
             out, left[-1] = out[sorter], left[-1][sorter]
 
         # build the multi-index w/ full levels
-        codes = list(map(lambda codes: np.repeat(codes[diff], nbin), codes[:-1]))
+        def build_codes(lev_codes: np.ndarray) -> np.ndarray:
+            return np.repeat(lev_codes[diff], nbin)
+
+        codes = [build_codes(lev_codes) for lev_codes in codes[:-1]]
         codes.append(left[-1])
 
         mi = MultiIndex(levels=levels, codes=codes, names=names, verify_integrity=False)

pandas/core/groupby/grouper.py

@@ -59,7 +59,7 @@ class Grouper:
         <http://pandas.pydata.org/pandas-docs/stable/user_guide/timeseries.html#offset-aliases>`_.
     axis : number/name of the axis, defaults to 0
     sort : bool, default to False
-        whether to sort the resulting codes
+        whether to sort the resulting labels
     closed : {'left' or 'right'}
         Closed end of interval. Only when `freq` parameter is passed.
     label : {'left' or 'right'}
@@ -378,11 +378,11 @@ def __repr__(self):
     def __iter__(self):
         return iter(self.indices)
 
-    _codes = None
-    _group_index = None
+    _codes = None  # type: np.ndarray
+    _group_index = None  # type: Index
 
     @property
-    def ngroups(self):
+    def ngroups(self) -> int:
         return len(self.group_index)
 
     @cache_readonly
@@ -395,24 +395,24 @@ def indices(self):
         return values._reverse_indexer()
 
     @property
-    def codes(self):
+    def codes(self) -> np.ndarray:
         if self._codes is None:
             self._make_codes()
         return self._codes
 
     @cache_readonly
-    def result_index(self):
+    def result_index(self) -> Index:
         if self.all_grouper is not None:
             return recode_from_groupby(self.all_grouper, self.sort, self.group_index)
         return self.group_index
 
     @property
-    def group_index(self):
+    def group_index(self) -> Index:
         if self._group_index is None:
             self._make_codes()
         return self._group_index
 
-    def _make_codes(self):
+    def _make_codes(self) -> None:
         if self._codes is None or self._group_index is None:
             # we have a list of groupers
             if isinstance(self.grouper, BaseGrouper):
@@ -425,7 +425,7 @@ def _make_codes(self):
             self._group_index = uniques
 
     @cache_readonly
-    def groups(self):
+    def groups(self) -> dict:
         return self.index.groupby(Categorical.from_codes(self.codes, self.group_index))