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from pyspark import since
from pyspark.rdd import PythonEvalType
from pyspark.sql.column import Column
from pyspark.sql.dataframe import DataFrame


class CoGroupedData(object):
    """
    A logical grouping of two :class:`GroupedData`,
    created by :func:`GroupedData.cogroup`.

    .. note:: Experimental

    .. versionadded:: 3.0
    """

    def __init__(self, gd1, gd2):
        self._gd1 = gd1
        self._gd2 = gd2
        self.sql_ctx = gd1.sql_ctx

    @since(3.0)
    def apply(self, udf):
        """
        Applies a function to each cogroup using a pandas udf and returns the result
        as a `DataFrame`.

        The user-defined function should take two `pandas.DataFrame` and return another
        `pandas.DataFrame`. For each side of the cogroup, 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 of arbitrary length and its schema must match the
        returnType of the pandas udf.

        .. note:: This function requires a full shuffle. All the data of a cogroup will be loaded
            into memory, so the user should be aware of the potential OOM risk if data is skewed
            and certain groups are too large to fit in memory.

        .. note:: Experimental

        :param udf: a cogrouped map user-defined function returned by
            :func:`pyspark.sql.functions.pandas_udf`.

        >>> from pyspark.sql.functions import pandas_udf, PandasUDFType
        >>> df1 = spark.createDataFrame(
        ...    [(20000101, 1, 1.0), (20000101, 2, 2.0), (20000102, 1, 3.0), (20000102, 2, 4.0)],
        ...    ("time", "id", "v1"))
        >>> df2 = spark.createDataFrame(
        ... [(20000101, 1, "x"), (20000101, 2, "y")],
        ... ("time", "id", "v2"))
        >>> @pandas_udf("time int, id int, v1 double, v2 string", PandasUDFType.COGROUPED_MAP)
        ... def asof_join(l, r):
        ...     return pd.merge_asof(l, r, on="time", by="id")
        >>> df1.groupby("id").cogroup(df2.groupby("id")).apply(asof_join).show()
        +--------+---+---+---+
        |    time| id| v1| v2|
        +--------+---+---+---+
        |20000101|  1|1.0|  x|
        |20000102|  1|3.0|  x|
        |20000101|  2|2.0|  y|
        |20000102|  2|4.0|  y|
        +--------+---+---+---+

        .. seealso:: :meth:`pyspark.sql.functions.pandas_udf`

        """
        # Columns are special because hasattr always return True
        if isinstance(udf, Column) or not hasattr(udf, 'func') \
           or udf.evalType != PythonEvalType.SQL_COGROUPED_MAP_PANDAS_UDF:
            raise ValueError("Invalid udf: the udf argument must be a pandas_udf of type "
                             "COGROUPED_MAP.")
        all_cols = self._extract_cols(self._gd1) + self._extract_cols(self._gd2)
        udf_column = udf(*all_cols)
        jdf = self._gd1._jgd.flatMapCoGroupsInPandas(self._gd2._jgd, udf_column._jc.expr())
        return DataFrame(jdf, self.sql_ctx)

    @staticmethod
    def _extract_cols(gd):
        df = gd._df
        return [df[col] for col in df.columns]
