Github user icexelloss commented on a diff in the pull request: https://github.com/apache/spark/pull/18732#discussion_r143506845 --- Diff: python/pyspark/sql/group.py --- @@ -192,7 +193,69 @@ def pivot(self, pivot_col, values=None): jgd = self._jgd.pivot(pivot_col) else: jgd = self._jgd.pivot(pivot_col, values) - return GroupedData(jgd, self.sql_ctx) + return GroupedData(jgd, self._df) + + @since(2.3) + def apply(self, udf): + """ + Maps each group of the current :class:`DataFrame` using a pandas udf and returns the result + as a :class:`DataFrame`. + + The user-defined function should take a `pandas.DataFrame` and return another + `pandas.DataFrame`. For each group, all columns are passed together as a `pandas.DataFrame` + to the user-function and the returned `pandas.DataFrame` are combined as a + :class:`DataFrame`. The returned `pandas.DataFrame` can be arbitrary length and its schema + must match the returnType of the pandas udf. + + :param udf: A wrapped udf function returned by :meth:`pyspark.sql.functions.pandas_udf` + + >>> from pyspark.sql.functions import pandas_udf + >>> df = spark.createDataFrame( + ... [(1, 1.0), (1, 2.0), (2, 3.0), (2, 5.0), (2, 10.0)], + ... ("id", "v")) + >>> @pandas_udf(returnType=df.schema) + ... def normalize(pdf): + ... v = pdf.v + ... return pdf.assign(v=(v - v.mean()) / v.std()) + >>> df.groupby('id').apply(normalize).show() # doctest: +SKIP + +---+-------------------+ + | id| v| + +---+-------------------+ + | 1|-0.7071067811865475| + | 1| 0.7071067811865475| + | 2|-0.8320502943378437| + | 2|-0.2773500981126146| + | 2| 1.1094003924504583| + +---+-------------------+ + + .. seealso:: :meth:`pyspark.sql.functions.pandas_udf` + + """ + from pyspark.sql.functions import pandas_udf + + # Columns are special because hasattr always return True + if isinstance(udf, Column) or not hasattr(udf, 'func') or not udf.vectorized: + raise ValueError("The argument to apply must be a pandas_udf") + if not isinstance(udf.returnType, StructType): + raise ValueError("The returnType of the pandas_udf must be a StructType") + + df = self._df + func = udf.func + returnType = udf.returnType --- End diff -- I actually like it because I think it's more readable this way.
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