feat: add unstack to series, add level param (#115)

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Fixes #<issue_number_goes_here> 🦕

Author: TrevorBergeron

bigframes/core/blocks.py

@@ -67,6 +67,10 @@
 _MONOTONIC_DECREASING = "monotonic_decreasing"
 
 
+LevelType = typing.Union[str, int]
+LevelsType = typing.Union[LevelType, typing.Sequence[LevelType]]
+
+
 class BlockHolder(typing.Protocol):
     """Interface for mutable objects with state represented by a block value object."""
 
@@ -1423,9 +1427,7 @@ def _get_unique_values(
             raise ValueError(f"Too many unique values: {pd_values}")
 
         if len(columns) > 1:
-            return pd.MultiIndex.from_frame(
-                pd_values.sort_values(by=list(pd_values.columns), na_position="first")
-            )
+            return pd.MultiIndex.from_frame(pd_values)
         else:
             return pd.Index(pd_values.squeeze(axis=1).sort_values(na_position="first"))
 
@@ -1611,6 +1613,24 @@ def cached(self) -> Block:
             index_labels=self.index_labels,
         )
 
+    def resolve_index_level(self, level: LevelsType) -> typing.Sequence[str]:
+        if utils.is_list_like(level):
+            levels = list(level)
+        else:
+            levels = [level]
+        resolved_level_ids = []
+        for level_ref in levels:
+            if isinstance(level_ref, int):
+                resolved_level_ids.append(self.index_columns[level_ref])
+            elif isinstance(level_ref, typing.Hashable):
+                matching_ids = self.index_name_to_col_id.get(level_ref, [])
+                if len(matching_ids) != 1:
+                    raise ValueError("level name cannot be found or is ambiguous")
+                resolved_level_ids.append(matching_ids[0])
+            else:
+                raise ValueError(f"Unexpected level: {level_ref}")
+        return resolved_level_ids
+
     def _is_monotonic(
         self, column_ids: typing.Union[str, Sequence[str]], increasing: bool
     ) -> bool:

bigframes/dataframe.py

@@ -1038,22 +1038,7 @@ def reorder_levels(self, order: LevelsType, axis: int | str = 0):
                 raise ValueError("Columns must be a multiindex to reorder levels.")
 
     def _resolve_levels(self, level: LevelsType) -> typing.Sequence[str]:
-        if utils.is_list_like(level):
-            levels = list(level)
-        else:
-            levels = [level]
-        resolved_level_ids = []
-        for level_ref in levels:
-            if isinstance(level_ref, int):
-                resolved_level_ids.append(self._block.index_columns[level_ref])
-            elif isinstance(level_ref, typing.Hashable):
-                matching_ids = self._block.index_name_to_col_id.get(level_ref, [])
-                if len(matching_ids) != 1:
-                    raise ValueError("level name cannot be found or is ambiguous")
-                resolved_level_ids.append(matching_ids[0])
-            else:
-                raise ValueError(f"Unexpected level: {level_ref}")
-        return resolved_level_ids
+        return self._block.resolve_index_level(level)
 
     def rename(self, *, columns: Mapping[blocks.Label, blocks.Label]) -> DataFrame:
         block = self._block.rename(columns=columns)
@@ -1802,20 +1787,25 @@ def _stack_multi(self, level: LevelsType = -1):
         block = block.stack(levels=len(level))
         return DataFrame(block)
 
-    def unstack(self):
+    def unstack(self, level: LevelsType = -1):
+        if isinstance(level, int) or isinstance(level, str):
+            level = [level]
+
         block = self._block
         # Special case, unstack with mono-index transpose into a series
         if self.index.nlevels == 1:
             block = block.stack(how="right", levels=self.columns.nlevels)
             return bigframes.series.Series(block)
 
-        # Pivot by last level of index
-        index_ids = block.index_columns
+        # Pivot by index levels
+        unstack_ids = self._resolve_levels(level)
         block = block.reset_index(drop=False)
-        block = block.set_index(index_ids[:-1])
+        block = block.set_index(
+            [col for col in self._block.index_columns if col not in unstack_ids]
+        )
 
         pivot_block = block.pivot(
-            columns=[index_ids[-1]],
+            columns=unstack_ids,
             values=self._block.value_columns,
             values_in_index=True,
         )

bigframes/series.py

@@ -352,22 +352,7 @@ def reorder_levels(self, order: LevelsType, axis: int | str = 0):
         return Series(self._block.reorder_levels(resolved_level_ids))
 
     def _resolve_levels(self, level: LevelsType) -> typing.Sequence[str]:
-        if _is_list_like(level):
-            levels = list(level)
-        else:
-            levels = [level]
-        resolved_level_ids = []
-        for level_ref in levels:
-            if isinstance(level_ref, int):
-                resolved_level_ids.append(self._block.index_columns[level_ref])
-            elif isinstance(level_ref, typing.Hashable):
-                matching_ids = self._block.index_name_to_col_id.get(level_ref, [])
-                if len(matching_ids) != 1:
-                    raise ValueError("level name cannot be found or is ambiguous")
-                resolved_level_ids.append(matching_ids[0])
-            else:
-                raise ValueError(f"Unexpected level: {level_ref}")
-        return resolved_level_ids
+        return self._block.resolve_index_level(level)
 
     def between(self, left, right, inclusive="both"):
         if inclusive not in ["both", "neither", "left", "right"]:
@@ -918,6 +903,29 @@ def argmin(self) -> int:
             scalars.Scalar, Series(block.select_column(row_nums)).iloc[0]
         )
 
+    def unstack(self, level: LevelsType = -1):
+        if isinstance(level, int) or isinstance(level, str):
+            level = [level]
+
+        block = self._block
+
+        if self.index.nlevels == 1:
+            raise ValueError("Series must have multi-index to unstack")
+
+        # Pivot by index levels
+        unstack_ids = self._resolve_levels(level)
+        block = block.reset_index(drop=False)
+        block = block.set_index(
+            [col for col in self._block.index_columns if col not in unstack_ids]
+        )
+
+        pivot_block = block.pivot(
+            columns=unstack_ids,
+            values=self._block.value_columns,
+            values_in_index=False,
+        )
+        return bigframes.dataframe.DataFrame(pivot_block)
+
     def idxmax(self) -> blocks.Label:
         block = self._block.order_by(
             [

tests/system/conftest.py

@@ -400,7 +400,11 @@ def hockey_df(
     hockey_table_id: str, session: bigframes.Session
 ) -> bigframes.dataframe.DataFrame:
     """DataFrame pointing at test data."""
-    return session.read_gbq(hockey_table_id)
+    return (
+        session.read_gbq(hockey_table_id)
+        .set_index(["player_name", "season"])
+        .sort_index()
+    )
 
 
 @pytest.fixture(scope="session")
@@ -419,7 +423,7 @@ def hockey_pandas_df() -> pd.DataFrame:
             "season": pd.Int64Dtype(),
         },
     )
-    df.index = df.index.astype("Int64")
+    df = df.set_index(["player_name", "season"]).sort_index()
     return df
 
 

tests/system/small/test_dataframe.py

@@ -1949,8 +1949,14 @@ def test_df_pivot(scalars_dfs, values, index, columns):
     ],
 )
 def test_df_pivot_hockey(hockey_df, hockey_pandas_df, values, index, columns):
-    bf_result = hockey_df.pivot(values=values, index=index, columns=columns).to_pandas()
-    pd_result = hockey_pandas_df.pivot(values=values, index=index, columns=columns)
+    bf_result = (
+        hockey_df.reset_index()
+        .pivot(values=values, index=index, columns=columns)
+        .to_pandas()
+    )
+    pd_result = hockey_pandas_df.reset_index().pivot(
+        values=values, index=index, columns=columns
+    )
 
     # Pandas produces NaN, where bq dataframes produces pd.NA
     pd.testing.assert_frame_equal(bf_result, pd_result, check_dtype=False)

tests/system/small/test_multiindex.py

@@ -909,13 +909,36 @@ def test_column_multi_index_reorder_levels(scalars_df_index, scalars_pandas_df_i
     pandas.testing.assert_frame_equal(bf_result, pd_result)
 
 
-def test_multi_index_unstack(hockey_df, hockey_pandas_df):
+@pytest.mark.parametrize(
+    ("level",),
+    [(["position", "team_name"],), ([-2, -1],), (["position"],), ("season",), (-3,)],
+)
+def test_df_multi_index_unstack(hockey_df, hockey_pandas_df, level):
     bf_result = (
-        hockey_df.set_index(["team_name", "season", "position"]).unstack().to_pandas()
+        hockey_df.set_index(["team_name", "position"], append=True)
+        .unstack(level=level)
+        .to_pandas()
     )
     pd_result = hockey_pandas_df.set_index(
-        ["team_name", "season", "position"]
-    ).unstack()
+        ["team_name", "position"], append=True
+    ).unstack(level=level)
+
+    pandas.testing.assert_frame_equal(bf_result, pd_result, check_dtype=False)
+
+
+@pytest.mark.parametrize(
+    ("level",),
+    [(["position", "team_name"],), ([-2, -1],), (["position"],), ("season",), (-3,)],
+)
+def test_series_multi_index_unstack(hockey_df, hockey_pandas_df, level):
+    bf_result = (
+        hockey_df.set_index(["team_name", "position"], append=True)["number"]
+        .unstack(level=level)
+        .to_pandas()
+    )
+    pd_result = hockey_pandas_df.set_index(["team_name", "position"], append=True)[
+        "number"
+    ].unstack(level=level)
 
     pandas.testing.assert_frame_equal(bf_result, pd_result, check_dtype=False)
 

third_party/bigframes_vendored/pandas/core/series.py

@@ -1654,6 +1654,19 @@ def clip(self):
         """
         raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
 
+    def unstack(self, level):
+        """
+        Unstack, also known as pivot, Series with MultiIndex to produce DataFrame.
+
+        Args:
+            level (int, str, or list of these, default last level):
+                Level(s) to unstack, can pass level name.
+
+        Returns:
+            DataFrame: Unstacked Series.
+        """
+        raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
+
     def argmax(self):
         """
         Return int position of the smallest value in the Series.