How To Reverse The Order Of LinkedHashMap Elements In Scala

Question

Is there any elegant way to reverse the elements' order of LinkedHashMap in Scala?

For instance, I have a LinkedHashMap[Integer, String] like:

[1, "one"]
[2, "two"]
[3, "three"]

What is the best way to get a LinkedHashMap[Integer, String] like:

[3, "three"]
[2, "two"]
[1, "one"]

score 1 · Answer 1 · answered Aug 09 '17 at 12:20

1

You can do

val reverse = for ((key, value) <- map) yield (value, key)

Note that this will not update the old LinkedHashMap, but will return a new one.

answered Aug 09 '17 at 12:20

Bruno

252
1
8

This reverses the keys and values; it doesn't reverse the order of the elements, which is what the OP wants. – Jeffrey Chung Aug 09 '17 at 12:57
indeed, I am looking for how to reverse the order of the entries of the map – ClassNotFoundException Aug 09 '17 at 13:59

score 1 · Accepted Answer · answered Aug 09 '17 at 13:12

1

import scala.collection.mutable.LinkedHashMap

val linked = LinkedHashMap(1 -> "one", 2 -> "two", 3 -> "three")

val reversed = LinkedHashMap(linked.toSeq.reverse: _*)
// reversed: scala.collection.mutable.LinkedHashMap[Int, String] = Map(3 -> three, 2 -> two, 1 -> one)

answered Aug 09 '17 at 13:12

Jeffrey Chung

19,319
8
34
54

Thank you. Discovered the '_*' for myself :) – ClassNotFoundException Aug 09 '17 at 16:09

How To Reverse The Order Of LinkedHashMap Elements In Scala

2 Answers2