Create a single collection from multiple collections in a way that maximises distance between elemen-CodePudding

Suppose you have the following data structure:

val words   = Seq("cat", "dog", "kid", "dee", "ding", "chip", "chord")
val grouped = words.groupBy(_.charAt(0))

What's a good functional way of creating another collection that's formed by taking each element of the sequences in grouped in round robin? I.e. something like this:

Seq("kid", "dog", "cat", "dee", "chip", "ding", "chord")

Seq("dog", "cat", "kid", "dee", "chip", "ding", "chord")

We do not know in advance how many sequences will be in grouped.

CodePudding user response：

You can flatten values using zipWithIndex to combine them with index inside every group then group by that index and flatten again:

grouped.values
    .flatMap(xs => xs.zipWithIndex)
    .groupBy(_._2)
    .values
    .flatMap(_.unzip._1)