Scala map and/or groupby functions

Question

I am new to Scala and I am trying to figure out some scala syntax.

So I have a list of strings.

wordList: List[String] = List("this", "is", "a", "test")

I have a function that returns a list of pairs that contains consonants and vowels counts per word:

def countFunction(words: List[String]): List[(String, Int)]

So, for example:

countFunction(List("test")) => List(('Consonants', 3), ('Vowels', 1))

I now want to take a list of words and group them by count signatures:

def mapFunction(words: List[String]): Map[List[(String, Int)], List[String]]

//using wordList from above
mapFunction(wordList) => List(('Consonants', 3), ('Vowels', 1)) -> Seq("this", "test")
                         List(('Consonants', 1), ('Vowels', 1)) -> Seq("is")
                         List(('Consonants', 0), ('Vowels', 1)) -> Seq("a")

I'm thinking I need to use GroupBy to do this:

def mapFunction(words: List[String]): Map[List[(String, Int)], List[String]] = { 
    words.groupBy(F: (A) => K)
}

I've read the scala api for Map.GroupBy and see that F represents discriminator function and K is the type of keys you want returned. So I tried this:

    words.groupBy(countFunction => List[(String, Int)]

However, scala doesn't like this syntax. I tried looking up some examples for groupBy and nothing seems to help me with my use case. Any ideas?

Solution

Based on your description, your count function should take a word instead of a list of words. I would have defined it like this:

def countFunction(words: String): List[(String, Int)]

If you do that you should be able to call words.groupBy(countFunction), which is the same as:

words.groupBy(word => countFunction(word))

If you cannot change the signature of countFunction, then you should be able to call group by like this:

words.groupBy(word => countFunction(List(word)))