How to count characters of a String?

Question

I am a pretty newbie to Scala! I would like to count the times a char occurs in a string. How do I do this? I started writing something like this but I find the syntax very hard to grasp. Any help?

 var s = "hello"
 var list = s.toList.distinct
 list.foreach(println(s.count(_=='list')))

Answer 1

You could try something like this if you wanted a Map of the chars to the counts:

val str = "hello"
val countsMap:Map[Char,Int] = 
  str.
    groupBy(identity).
    mapValues(_.size)

Which would expand to the more longhand form:

str.
  groupBy(c => c).
  mapValues(str => str.size)

So to break this down, in the groupBy we are saying that we want to group by the individual Chars in the String themselves. This will produce a Map[Char, String] like so:

Map(e -> e, h -> h, l -> ll, o -> o)

Then, you re-map the values portion of that Map with the mapValues method telling it to use the .size of the String and not the String itself.