feat: Add Series.dt.day_name (#2218)

Author: TrevorBergeron

bigframes/operations/datetimes.py

@@ -148,6 +148,9 @@ def unit(self) -> str:
         # Assumption: pyarrow dtype
         return self._data._dtype.pyarrow_dtype.unit
 
+    def day_name(self) -> series.Series:
+        return self.strftime("%A")
+
     def strftime(self, date_format: str) -> series.Series:
         return self._data._apply_unary_op(ops.StrftimeOp(date_format=date_format))
 

tests/system/small/operations/test_datetimes.py

@@ -123,6 +123,21 @@ def test_dt_dayofyear(scalars_dfs, col_name):
     assert_series_equal(pd_result, bf_result, check_dtype=False)
 
 
+@pytest.mark.parametrize(
+    ("col_name",),
+    DATE_COLUMNS,
+)
+def test_dt_day_name(scalars_dfs, col_name):
+    pytest.importorskip("pandas", minversion="2.0.0")
+    scalars_df, scalars_pandas_df = scalars_dfs
+    bf_series: bigframes.series.Series = scalars_df[col_name]
+
+    bf_result = bf_series.dt.day_name().to_pandas()
+    pd_result = scalars_pandas_df[col_name].dt.day_name()
+
+    assert_series_equal(pd_result, bf_result, check_dtype=False)
+
+
 @pytest.mark.parametrize(
     ("col_name",),
     DATE_COLUMNS,

third_party/bigframes_vendored/pandas/core/indexes/accessor.py

@@ -91,6 +91,30 @@ def day_of_week(self):
 
         raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
 
+    @property
+    def day_name(self):
+        """
+        Return the day names in english.
+
+        **Examples:**
+            >>> s = bpd.Series(pd.date_range(start="2018-01-01", freq="D", periods=3))
+            >>> s
+            0    2018-01-01 00:00:00
+            1    2018-01-02 00:00:00
+            2    2018-01-03 00:00:00
+            dtype: timestamp[us][pyarrow]
+            >>> s.dt.day_name()
+            0       Monday
+            1      Tuesday
+            2    Wednesday
+            dtype: string
+
+        Returns:
+            Series: Series of day names.
+
+        """
+        raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
+
     @property
     def dayofyear(self):
         """The ordinal day of the year.