CODEWITHSUNDEEP
scala
keegan
keegan

Reputation: 2992

scala count letter pairs in word

I'm new to learning Scala and would appreciate any thoughts on an idiomatic way to do the following. I want to count occurrences of sequential letter pairs in a word.

For example, for the word "home", the output might be Map("ho"->1,"om"->1,"me"->1). And for 'lulu', the result would be Map("lu"->2, "ul"->1 ).

So performing a simple single-letter count might be done as 

"abracadabra".map(s => s).groupBy(identity).mapValues(_.length)

But I'm stumped as to how to add-in the two-letter component of this problem. Thanks for your thoughts.

Upvotes: 3

Views: 228

Answers (2)

Marth
Marth

Reputation: 24812

You can use .sliding :

scala> "abracadabra".sliding(2).toList.groupBy(identity).mapValues(_.length)
res3: scala.collection.immutable.Map[String,Int] = 
        Map(br -> 2, ca -> 1, ab -> 2, ra -> 2, ac -> 1, da -> 1, ad -> 1)

scala> "lulu".sliding(2).toList.groupBy(identity).mapValues(_.length)
res4: scala.collection.immutable.Map[String,Int] = Map(ul -> 1, lu -> 2)

From the docs :

Sliding : Groups elements in fixed size blocks by passing a "sliding window" over them

Upvotes: 6

dhg
dhg

Reputation: 52681

You should use sliding(2):

"abracadabra".sliding(2).toVector.map(s => s).groupBy(identity).mapValues(_.length)
// Map(br -> 2, ca -> 1, ab -> 2, ra -> 2, ac -> 1, da -> 1, ad -> 1)

Upvotes: 1

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