zipWithIndex with and without case

Question

How are the following 2 pieces of code equivalent? (how does case work)

 list.zipWithIndex.flatMap{ 
     rowAndIndex =>
     rowAndIndex._1.zipWithIndex
}

and

list.zipWithIndex.flatMap {
    case (rowAndIndex, r) =>
     rowAndIndex.zipWithIndex
}

Answer 1

You are probably confused by wrong names in second sample. I changed it to:

list.zipWithIndex.flatMap {
    case (row, index) =>
     row.zipWithIndex
}

This is short version of:

list.zipWithIndex.flatMap { rowAndIndex => 
  rowAndIndex match {
    case (row, index) => row.zipWithIndex
  }
}

Answer 2

I preferred the first one, since every element here is case (rowAndIndex, r), check it every time seems unnecessary.

And, it seems that you actually don't want the first 'index', why not just use:

list.map(s => s.zipWithIndex).flatten

By the way, I just put following code to http://scalass.com/tryout

val list = List("Abby", "Jim", "Tony")

val a = list.zipWithIndex.flatMap({a =>
  a._1.zipWithIndex})
println(a)

val b = list.zipWithIndex.flatMap({case (rowAndIndex, r) =>
  rowAndIndex.zipWithIndex})
println(b)

val d = list.map(s => s.zipWithIndex).flatten
println(d)

The output is all like

List((A,0), (b,1), (b,2), (y,3), (J,0), (i,1), (m,2), (T,0), (o,1), (n,2), (y,3))

This is what you want, right?