Apache-Spark : What is map(_._2) shorthand for?

Question

I read a project\'s source code, found:

val sampleMBR = inputMBR.map(_._2).sample

inputMBR is a tuple.

the function

Answer 1

Two underscores in '_._2' are different.

First '_' is for placeholder of anonymous function; Second '_2' is member of case class Tuple.

Something like:

case class Tuple3 (_1: T1, _2: T2, _3: T3) {...}