from pyspark.sql.types import StructType, StructField, StringType, DateType, DoubleType

schema = StructType(

                    [StructField('ds', DateType()),

                     StructField('store_id', StringType()),

                     StructField('dept_id', StructType()),

                     StructField('y', DoubleType()),

                     StructField('yhat', DoubleType())]

                    )