FIX-#1426: Groupby on categories fixed

Signed-off-by: Dmitry Chigarev <dmitry.chigarev@intel.com>

modin/backends/pandas/query_compiler.py

@@ -2029,6 +2029,11 @@ def _callable_func(self, func, axis, *args, **kwargs):
     )
 
     def groupby_agg(self, by, axis, agg_func, groupby_args, agg_args, drop=False):
+        # since we're going to modify `groupby_args` dict in a `groupby_agg_builder`,
+        # we want to copy it to not propagate these changes into source dict, in case
+        # of unsuccessful end of function
+        groupby_args = groupby_args.copy()
+
         as_index = groupby_args.get("as_index", True)
 
         def groupby_agg_builder(df):

modin/data_management/functions/groupby_function.py

@@ -40,14 +40,21 @@ def caller(
                 )
             else:
                 qc = query_compiler
+            # since we're going to modify `groupby_args` dict in a `compute_map`,
+            # we want to copy it to not propagate these changes into source dict, in case
+            # of unsuccessful end of function
+            groupby_args = groupby_args.copy()
+
             as_index = groupby_args.get("as_index", True)
+            observed = groupby_args.get("observed", False)
 
             def _map(df, other):
                 def compute_map(df, other):
                     # Set `as_index` to True to track the metadata of the grouping object
                     # It is used to make sure that between phases we are constructing the
                     # right index and placing columns in the correct order.
                     groupby_args["as_index"] = True
+                    groupby_args["observed"] = True
                     other = other.squeeze(axis=axis ^ 1)
                     if isinstance(other, pandas.DataFrame):
                         df = pandas.concat(
@@ -57,6 +64,20 @@ def compute_map(df, other):
                     result = map_func(
                         df.groupby(by=other, axis=axis, **groupby_args), **map_args
                     )
+                    # if `other` has category dtype, then pandas will drop that
+                    # column after groupby, inserting it back to correctly process
+                    # reduce phase
+                    if (
+                        drop
+                        and not as_index
+                        and isinstance(other, pandas.Series)
+                        and isinstance(other.dtype, pandas.CategoricalDtype)
+                        and result.index.name is not None
+                        and result.index.name not in result.columns
+                    ):
+                        result.insert(
+                            loc=0, column=result.index.name, value=result.index
+                        )
                     # The _modin_groupby_ prefix indicates that this is the first partition,
                     # and since we may need to insert the grouping data in the reduce phase
                     if (
@@ -82,6 +103,7 @@ def compute_reduce(df):
                     df = df.reset_index(drop=False)
                     # See note above about setting `as_index`
                     groupby_args["as_index"] = as_index
+                    groupby_args["observed"] = observed
                     if other_len > 1:
                         by_part = list(df.columns[0:other_len])
                     else:
@@ -98,7 +120,7 @@ def compute_reduce(df):
                     if isinstance(by_part, str) and by_part in result.columns:
                         if "_modin_groupby_" in by_part and drop:
                             col_name = by_part[len("_modin_groupby_") :]
-                            new_result = result.drop(columns=col_name)
+                            new_result = result.drop(columns=col_name, errors="ignore")
                             new_result.columns = [
                                 col_name if "_modin_groupby_" in c else c
                                 for c in new_result.columns

modin/pandas/groupby.py

@@ -128,7 +128,7 @@ def _index_grouped(self):
                 }
             else:
                 if isinstance(self._by, type(self._query_compiler)):
-                    by = self._by.to_pandas().squeeze()
+                    by = self._by.to_pandas().squeeze().values
                 else:
                     by = self._by
                 if self._axis == 0:
@@ -433,7 +433,7 @@ def size(self):
             series_result = Series(query_compiler=result._query_compiler)
             # Pandas does not name size() output
             series_result.name = None
-            return series_result
+            return series_result.fillna(0)
         else:
             return DataFrameGroupBy(
                 self._df.T,
@@ -529,12 +529,16 @@ def fillna(self, **kwargs):
         return result
 
     def count(self, **kwargs):
-        return self._wrap_aggregation(
+        result = self._wrap_aggregation(
             type(self._query_compiler).groupby_count,
             lambda df, **kwargs: df.count(**kwargs),
             numeric_only=False,
             **kwargs,
         )
+        # pandas do it in case of Series
+        if isinstance(result, Series):
+            result = result.fillna(0)
+        return result
 
     def pipe(self, func, *args, **kwargs):
         return com.pipe(self, func, *args, **kwargs)

modin/pandas/test/test_groupby.py

@@ -21,18 +21,28 @@
     check_df_columns_have_nans,
     create_test_dfs,
     eval_general,
+    df_categories_equals,
 )
 
 pd.DEFAULT_NPARTITIONS = 4
 
 
 def modin_df_almost_equals_pandas(modin_df, pandas_df):
-    difference = to_pandas(modin_df) - pandas_df
+    df_categories_equals(modin_df._to_pandas(), pandas_df)
+
+    modin_df = to_pandas(modin_df)
+
+    if hasattr(modin_df, "select_dtypes"):
+        modin_df = modin_df.select_dtypes(exclude=["category"])
+    if hasattr(pandas_df, "select_dtypes"):
+        pandas_df = pandas_df.select_dtypes(exclude=["category"])
+
+    difference = modin_df - pandas_df
     diff_max = difference.max()
     if isinstance(diff_max, pandas.Series):
         diff_max = diff_max.max()
     assert (
-        to_pandas(modin_df).equals(pandas_df)
+        modin_df.equals(pandas_df)
         or diff_max < 0.0001
         or (all(modin_df.isna().all()) and all(pandas_df.isna().all()))
     )
@@ -234,7 +244,8 @@ def test_mixed_dtypes_groupby(as_index):
     ],
 )
 @pytest.mark.parametrize("as_index", [True, False])
-def test_simple_row_groupby(by, as_index):
+@pytest.mark.parametrize("col1_category", [True, False])
+def test_simple_row_groupby(by, as_index, col1_category):
     pandas_df = pandas.DataFrame(
         {
             "col1": [0, 1, 2, 3],
@@ -245,6 +256,9 @@ def test_simple_row_groupby(by, as_index):
         }
     )
 
+    if col1_category:
+        pandas_df = pandas_df.astype({"col1": "category"})
+
     modin_df = from_pandas(pandas_df)
     n = 1
     modin_groupby = modin_df.groupby(by=by, as_index=as_index)
@@ -267,10 +281,10 @@ def test_simple_row_groupby(by, as_index):
     eval_ndim(modin_groupby, pandas_groupby)
     if not check_df_columns_have_nans(modin_df, by):
         # cum* functions produce undefined results for columns with NaNs so we run them only when "by" columns contain no NaNs
-        eval_cumsum(modin_groupby, pandas_groupby)
-        eval_cummax(modin_groupby, pandas_groupby)
-        eval_cummin(modin_groupby, pandas_groupby)
-        eval_cumprod(modin_groupby, pandas_groupby)
+        eval_general(modin_groupby, pandas_groupby, lambda df: df.cumsum(axis=0))
+        eval_general(modin_groupby, pandas_groupby, lambda df: df.cummax(axis=0))
+        eval_general(modin_groupby, pandas_groupby, lambda df: df.cummin(axis=0))
+        eval_general(modin_groupby, pandas_groupby, lambda df: df.cumprod(axis=0))
 
     eval_general(
         modin_groupby,
@@ -312,7 +326,7 @@ def test_simple_row_groupby(by, as_index):
         modin_df_almost_equals_pandas,
         is_default=True,
     )
-    eval_rank(modin_groupby, pandas_groupby)
+    eval_general(modin_groupby, pandas_groupby, lambda df: df.rank())
     eval_max(modin_groupby, pandas_groupby)
     eval_len(modin_groupby, pandas_groupby)
     eval_sum(modin_groupby, pandas_groupby)
@@ -332,7 +346,12 @@ def test_simple_row_groupby(by, as_index):
         # Pandas groupby.transform does not work correctly with NaN values in grouping columns. See Pandas bug 17093.
         transform_functions = [lambda df: df + 4, lambda df: -df - 10]
         for func in transform_functions:
-            eval_transform(modin_groupby, pandas_groupby, func)
+            eval_general(
+                modin_groupby,
+                pandas_groupby,
+                lambda df: df.transform(func),
+                check_exception_type=None,
+            )
 
     pipe_functions = [lambda dfgb: dfgb.sum()]
     for func in pipe_functions:
@@ -347,7 +366,9 @@ def test_simple_row_groupby(by, as_index):
     )
     eval_fillna(modin_groupby, pandas_groupby)
     eval_count(modin_groupby, pandas_groupby)
-    eval_size(modin_groupby, pandas_groupby)
+    eval_general(
+        modin_groupby, pandas_groupby, lambda df: df.size(), check_exception_type=None
+    )
     eval_general(modin_groupby, pandas_groupby, lambda df: df.tail(n), is_default=True)
     eval_quantile(modin_groupby, pandas_groupby)
     eval_general(modin_groupby, pandas_groupby, lambda df: df.take(), is_default=True)
@@ -471,14 +492,19 @@ def test_single_group_row_groupby():
     eval_groups(modin_groupby, pandas_groupby)
 
 
-def test_large_row_groupby():
+@pytest.mark.parametrize("is_by_category", [True, False])
+def test_large_row_groupby(is_by_category):
     pandas_df = pandas.DataFrame(
         np.random.randint(0, 8, size=(100, 4)), columns=list("ABCD")
     )
 
     modin_df = from_pandas(pandas_df)
 
     by = [str(i) for i in pandas_df["A"].tolist()]
+
+    if is_by_category:
+        by = pandas.Categorical(by)
+
     n = 4
 
     modin_groupby = modin_df.groupby(by=by)

modin/pandas/test/utils.py

@@ -381,8 +381,17 @@ def categories_equals(left, right):
 
 
 def df_categories_equals(df1, df2):
-    categories_columns = df1.select_dtypes(include="category").columns
+    if not hasattr(df1, "select_dtypes"):
+        if isinstance(df1, pandas.CategoricalDtype):
+            return categories_equals(df1, df2)
+        elif isinstance(getattr(df1, "dtype"), pandas.CategoricalDtype) and isinstance(
+            getattr(df1, "dtype"), pandas.CategoricalDtype
+        ):
+            return categories_equals(df1.dtype, df2.dtype)
+        else:
+            return True
 
+    categories_columns = df1.select_dtypes(include="category").columns
     for column in categories_columns:
         is_category_ordered = df1[column].dtype.ordered
         assert_categorical_equal(
@@ -558,17 +567,27 @@ def check_df_columns_have_nans(df, cols):
 
 
 def eval_general(
-    modin_df, pandas_df, operation, comparator=df_equals, __inplace__=False, **kwargs
+    modin_df,
+    pandas_df,
+    operation,
+    comparator=df_equals,
+    __inplace__=False,
+    check_exception_type=True,
+    **kwargs,
 ):
     md_kwargs, pd_kwargs = {}, {}
 
     def execute_callable(fn, inplace=False, md_kwargs={}, pd_kwargs={}):
         try:
             pd_result = fn(pandas_df, **pd_kwargs)
-        except Exception as e:
-            with pytest.raises(type(e)):
+        except Exception as pd_e:
+            if check_exception_type is None:
+                return None
+            with pytest.raises(Exception) as md_e:
                 # repr to force materialization
                 repr(fn(modin_df, **md_kwargs))
+            if check_exception_type:
+                assert isinstance(md_e.value, type(pd_e))
         else:
             md_result = fn(modin_df, **md_kwargs)
             return (md_result, pd_result) if not __inplace__ else (modin_df, pandas_df)