How to make function for flatten pairs of arrays in Scala? - scala

Question

if i have
scala> test
res3: Array[java.io.Serializable] = Array(Array((AA,BB), (CC,DD)), (EE,FF))
and i want to convert this to
Array[(Any, Any)] = Array((AA,BB), (CC,DD), (EE,FF))
I can convert using flatMap function like this
scala> val test2 = test.flatMap{
| case (a,b) => Array((a,b))
| case i:Array[Any] => i.flatMap{
| case (a,b)=> Array((a,b))}
| }
test2: Array[(Any, Any)] = Array((AA,BB), (CC,DD), (EE,FF))
but I want to make function for All depth of Arrays.
so I tried
scala> def flatArray(array: Array[Any]): Array[(Any,Any)] ={
| array.flatMap{
| case (a,b) => Array((a,b))
| case i:Array[Any] => flatArray(i)
| }
| }
scala> val test2 = flatArray(test)
<console>:9: error: type mismatch;
found : Array[java.io.Serializable]
required: Array[Any]
Note: java.io.Serializable <: Any, but class Array is invariant in type T.
You may wish to investigate a wildcard type such as `_ <: Any`. (SLS 3.2.10)
val test2 = flatArray(test)
^
what's the problem ???

Answer 1

You can do flattening the following way:
def flatten(arr:Array[Any]):Array[(Any,Any)] =
arr.flatMap {
case (a,b) => Array((a,b))
case v:Array[Any] => flatten(v)
}

Answer 2

Well, I have a solution, maybe not the best one, since it uses non-tail recursion that may lead to a problems when you have a lot of data. Also, it assumes, that you don't have mixed tuples and arrays on the same level (like Array(1 -> 2, Array(2 -> 3)). So, just for reference:
import scala.collection.mutable.ArrayBuffer
val a: Array[Any] =
Array(
Array(1 -> 2, 2 -> 3),
Array(
Array(7 -> 1, 8 -> 3),
Array(
Array(1 -> 4, 5 -> 6, 12 -> 5),
Array(3 -> 4)
)
)
)
def flattenImpl(arr: Array[Any], acc: ArrayBuffer[(Int, Int)]): Array[(Int, Int)] = {
arr.headOption match {
case None => acc.toArray
case Some((a: Int, b:Int)) => flattenImpl(arr.tail, acc :+ a -> b)
case Some(a: Array[Any]) => flattenImpl(a, acc ++ flattenImpl(arr.tail, acc))
}
}
def flatten(arr: Array[Any]): Array[(Int, Int)] = flattenImpl(arr, ArrayBuffer())
val res = flatten(a)
res: Array[(Int, Int)] = Array((3,4), (1,4), (5,6), (12,5), (7,1), (8,3), (1,2), (2,3))