scala - How to convert keys in a Map to lower case?

Question

I have a map where the key is a String and I need to change every key to lower case before work with this map.

How can I do it in Scala? I was thinking something like:

var newMap = scala.collection.mutable.Map[String, String]()
data.foreach(d => newMap +=(d._1.toLowerCase -> d._2))   

What is the best approach for it? Thanks in advance.

Answer 1

The problem here is that you're trying to add the lower-cased keys to the mutable Map, which is just going to pile additional keys into it. It would be better to just use a strict map here, rather than a side-effecting function.

val data = scala.collection.mutable.Map[String, String]("A" -> "1", "Bb" -> "aaa")
val newData = data.map { case (key, value) => key.toLowerCase -> value }

If you really want to do it in a mutable way, then you have to remove the old keys.

data.foreach { case (key, value) =>
    data -= key
    data += key.toLowerCase -> value
}

scala> data
res79: scala.collection.mutable.Map[String,String] = Map(bb -> aaa, a -> 1)