question: public OptionalDouble minByDouble ( DoubleUnaryOperator keyExtractor ) { double [ ] result = collect ( null , null , null ) ; return result [ 2 ] == 1 ? OptionalDouble . of ( result [ 0 ] ) : OptionalDouble . empty ( ) ; }
target:  Returns the minimum element of this stream according to the provided key extractor function. <p> This is a terminal operation.