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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _prep_spark_sql_groupby(self):
 """Used Spark SQL group approach"""

        # Strip the index info
        non_index_columns = filter(lambda x: x not in self._prdd._index_names,
                                   self._prdd._column_names())
        self._grouped_spark_sql = (self._prdd.to_spark_sql()
                                   .select(non_index_columns)
                                   .groupBy(self._by))
        self._columns = filter(lambda x: x != self._by,
                               non_index_columns)