FEAT: Add initial partial support for groupby.cumcount() (modin-proje…

…ct#54)

* FEAT: Add partial support for cumcount

* Remove the set_index_name

* Squeeze the result

* Write cumcount name to None

* Can't set dtype to int64

modin/core/execution/client/query_compiler.py

@@ -911,6 +911,7 @@ def forwarding_method(self, by, *args, **kwargs):
         "any",
         "size",
         "skew",
+        "cumcount",
         "cumsum",
         "cummax",
         "cummin",

modin/core/storage_formats/base/query_compiler.py

@@ -2596,6 +2596,30 @@ def groupby_skew(
             drop=drop,
         )
 
+    @doc_utils.doc_groupby_method(
+        action="compute cumulative count",
+        result="count of all the previous values",
+        refer_to="cumcount",
+    )
+    def groupby_cumcount(
+        self,
+        by,
+        axis,
+        groupby_kwargs,
+        agg_args,
+        agg_kwargs,
+        drop=False,
+    ):
+        return self.groupby_agg(
+            by=by,
+            agg_func="cumcount",
+            axis=axis,
+            groupby_kwargs=groupby_kwargs,
+            agg_args=agg_args,
+            agg_kwargs=agg_kwargs,
+            drop=drop,
+        )
+
     @doc_utils.doc_groupby_method(
         action="compute cumulative sum",
         result="sum of all the previous values",

modin/pandas/groupby.py

@@ -832,9 +832,15 @@ def pipe(self, func, *args, **kwargs):
         return com.pipe(self, func, *args, **kwargs)
 
     def cumcount(self, ascending=True):
-        result = self._default_to_pandas(lambda df: df.cumcount(ascending=ascending))
-        # pandas does not name the index on cumcount
-        result._query_compiler.set_index_name(None)
+        result = self._wrap_aggregation(
+            type(self._query_compiler).groupby_cumcount,
+            numeric_only=False,
+            agg_kwargs=dict(ascending=ascending),
+        )
+        if not isinstance(result, Series):
+            # The result should always be a Series with name None and type int64
+            result = result.squeeze(axis=1)
+            result.name = None
         return result
 
     def tail(self, n=5):