question: average aggregate function . concode_field_sep PlaceHolder placeHolder concode_field_sep TypedColumn<T,Long> sumLong concode_elem_sep TypedColumn<T,Long> count concode_elem_sep TypedColumn<T,Double> sum
target: TypedColumn < T , Double > function ( MapFunction < T , Double > arg0 ) { return new TypedAverage < T > ( arg0 ) . toColumnJava ( ) ; }