itholic commented on a change in pull request #33858:
URL: https://github.com/apache/spark/pull/33858#discussion_r704045118



##########
File path: python/pyspark/pandas/series.py
##########
@@ -4475,6 +4477,146 @@ def replace(
 
         return self._with_new_scol(current)  # TODO: dtype?
 
+    def combine(
+        self,
+        other: "Series",
+        func: Callable,
+        fill_value: Optional[Any] = None,
+        return_type: Union[Union[AtomicType, str], ArrayType] = "string",
+    ) -> "Series":
+        """
+        Combine the Series with a Series or scalar according to `func`.
+        Combine the Series and `other` using `func` to perform elementwise
+        selection for combined Series.
+        `fill_value` is assumed when value is missing at some index
+        from one of the two objects being combined.
+
+        .. versionadded:: 3.3.0
+
+        Parameters
+        ----------
+        other : Series or scalar
+            The value(s) to be combined with the `Series`.
+        func : function
+            Function that takes two scalars as inputs and returns an element.
+        fill_value : scalar, optional
+            The value to assume when an index is missing from
+            one Series or the other. The default specifies to use the
+            appropriate NaN value for the underlying dtype of the Series.
+        return_type : :class:`pyspark.sql.types.DataType` or str
+            the return type of the output Series. The value can be either a
+            :class:`pyspark.sql.types.DataType` object or a DDL-formatted type 
string.
+
+        Returns
+        -------
+        Series
+            The result of combining the Series with the other object.
+
+        See Also
+        --------
+        Series.combine_first : Combine Series values, choosing the calling
+            Series' values first.
+
+        Examples
+        --------
+        Consider 2 Datasets ``s1`` and ``s2`` containing
+        highest clocked speeds of different birds.
+
+        >>> from pyspark.pandas.config import set_option, reset_option
+        >>> set_option("compute.ops_on_diff_frames", True)
+        >>> s1 = ps.Series({'falcon': 330.0, 'eagle': 160.0})
+        >>> s1
+        falcon    330.0
+        eagle     160.0
+        dtype: float64
+        >>> s2 = ps.Series({'falcon': 345.0, 'eagle': 200.0, 'duck': 30.0})
+        >>> s2
+        falcon    345.0
+        eagle     200.0
+        duck       30.0
+        dtype: float64
+
+        Now, to combine the two datasets and view the highest speeds
+        of the birds across the two datasets
+
+        >>> s1.combine(s2, max, return_type="double")
+        duck        NaN
+        eagle     200.0
+        falcon    345.0
+        dtype: float64
+
+        In the previous example, the resulting value for duck is missing,
+        because the maximum of a NaN and a float is a NaN.
+        So, in the example, we set ``fill_value=0``,
+        so the maximum value returned will be the value from some dataset.
+
+        >>> s1.combine(s2, max, fill_value=0, return_type="double")
+        duck       30.0
+        eagle     200.0
+        falcon    345.0
+        dtype: float64
+        >>> reset_option("compute.ops_on_diff_frames")
+        """
+        if not isinstance(other, Series) and not np.isscalar(other):
+            raise TypeError("unsupported type: %s" % type(other))
+
+        tmp_other_col = verify_temp_column_name(self._internal.spark_frame, 
"__tmp_other_col__")
+        if np.isscalar(other):
+            combined = DataFrame(
+                InternalFrame(
+                    spark_frame=self._internal.spark_frame.select(
+                        *self._internal.spark_columns
+                    ).withColumn(tmp_other_col, SF.lit(other)),
+                    index_spark_columns=self._internal.index_spark_columns,
+                )
+            )
+        elif same_anchor(self, other):
+            combined = self._psdf[self._column_label, other._column_label]
+        elif fill_value is None:
+            combined = combine_frames(self.to_frame(), other.to_frame())
+        else:
+            combined = self._combine_frame_with_fill_value(other, 
fill_value=fill_value)
+
+        @pandas_udf(returnType=return_type)  # type: ignore
+        def wrapped_func(x: pd.Series, y: pd.Series) -> pd.Series:
+            return x.combine(y, func)
+
+        internal = InternalFrame(
+            spark_frame=combined._internal.spark_frame.select(
+                *combined._internal.index_spark_columns,
+                wrapped_func(*combined._internal.data_spark_columns),
+                NATURAL_ORDER_COLUMN_NAME
+            ),
+            index_spark_columns=combined._internal.index_spark_columns,
+            column_labels=self._internal.column_labels if np.isscalar(other) 
else [None],
+            column_label_names=[None],
+        )

Review comment:
       Oh, yeah it's my mistake.
   
   I think we should get a return type from the function, not `self`.
   
   Let's try to use the `infer_return_type`.
   
   For example,
   
   ```python
           return_type = infer_return_type(func).spark_type
   
           @pandas_udf(returnType=return_type)  # type: ignore
           def wrapped_func(x: pd.Series, y: pd.Series) -> pd.Series:
               return x.combine(y, func)
   ```
   
   Also, can you refer the implementation for `Series.apply` ??
   
   I think that might be a hint for this implementation.




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