scala for every first element in a list of tuples get max of the second element

Question

I have a list of tuples like below

List((a,1), (a,2), (b,2), (b,1))

I want to create a List like below from that above list

List((a,2), (b,2))

Only one first element and MAX of the second element. How can I do this concisely?

Trying this list.groupBy(._1).map { case (common, lst) => (common, lst.reduce( max _)) } — yalkris
– yalkris, Commented Aug 29, 2017 at 23:29
@Dima Pressed return before I entered my full comment. This is what I am getting when I tried error: value max is not a member of (String, Int) — yalkris
– yalkris, Commented Aug 29, 2017 at 23:37
This worked myList.groupBy(._1).map {case (common, lst) => lst.maxBy(._2) }.toList — yalkris
– yalkris, Commented Aug 29, 2017 at 23:51

Leo C · Accepted Answer · 2017-08-29 23:50:38Z

1

Since you only need the 1st elements of same value once along with the max value of the corresponding 2nd element, it's no difference from rephrasing the question as for every distinct 1st element in the tuple list, list the max 2nd element:

val l = List(("a",1), ("a",2), ("b",2), ("b",1))

l.groupBy(_._1).
  mapValues( _.map(_._2).max ).
  toList
// res1: List[(String, Int)] = List((b,2), (a,2))

answered Aug 29, 2017 at 23:50

Leo C

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1 Comment

yalkris Over a year ago

Perfect. Even better.

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