CODEWITHSUNDEEP
scala
kingledion
kingledion

Reputation: 2510

How to get a list of indexes from list of counts?

Given an input sequence:

Array[Int] = Array(0, 1, 0, 2, 1, 0)

I want a list that gives me indexes of each entry times, the number of times for each entry in the sequence. The output here would be:

Array[Int] = Array(1, 3, 3, 4)

There is one instance of index 1, two instances of index 3, one instance of index 4. How can write a function to do this in scala?

Here is one attempt, but I 

val func1 = (cnt: Int, idx: Int) => Array.fill(cnt)(idx)
countarray.zipWithIndex.map(func1)

func1: (Int, Int) => Array[Int] = <function2>
<console>:132: error: type mismatch;
 found   : (Int, Int) => Array[Int]
 required: ((Int, Int)) => ?
              seq_of_vectors.map(_.numNonzeros).zipWithIndex.map(func1)

Upvotes: 0

Views: 68

Answers (1)

jwvh
jwvh

Reputation: 51271

You're quite close.

arr.zipWithIndex.flatMap{case (rep,idx) => Array.fill(rep)(idx)}

Use flatMap() so that all the intermediate Arrays will be flattened into one Array result.

Upvotes: 4

Related Questions