How can I combine two arrays into one array in Kotlin?

Question

I want to make one array from two arrays.

I tried to do use +:

var array1 = intArrayOf(1,2,3)
var array2 = intArrayOf(4,5,6)
var array3 = array1 + array2

But it is not working unfortunately... How can I combine them?

Answer 1

Actually, your exact code works for me. Tried it on multiple Kotlin versions. You can find the operator fun IntArray.plus(elements: IntArray): IntArray function that's being used for this in the docs here, and its source here.

var array1 = intArrayOf(1, 2, 3)        // 1, 2, 3
var array2 = intArrayOf(4, 5, 6)        // 4, 5 ,6
var array3 = array1 + array2            // 1, 2, 3, 4, 5, 6

---

Are you perhaps looking to do something different, like add the elements one by one and create a new array of length 3? You can do that like this:

val array4 = array1.zip(array2, Int::plus).toTypedArray()    // 5, 7, 9

The extra toTypedArray call is necessary only if you actually need an array, otherwise you can use the List<Int> that the zip function returns.

Answer 2

Using the spread operator:

var array3 = intArrayOf(*array1, *array2)

This could be especially useful when you need to add some custom elements between the arrays, like intArrayOf(7, *array1, 8, 9, *array2, 10, 11).

Note spreading is much more efficient than plus-ing, because it creates only one resulting array. Using an equivalent plus version of the above spread example may use 5x more space and take 5x more time.

Answer 3

I am adding some other ways to merge two arrays.

var array1 = intArrayOf(1, 2, 3)
var array2 = intArrayOf(4, 5, 6)

Way 1:

var array3 = array1 + array2
print(array3.asList())

It will print [1, 2, 3, 4, 5, 6]. This one is given above.

You can replace the + by plus() method.

var array3 = array1.plus(array2)
print(array3.asList())

It will also work the same. When you are using +, at that time it actually calls the plus() method.

Way 2:

var array3 = array1.union(array2.asList())
print(array3)

It will print [1, 2, 3, 4, 5, 6].

union() method can take a collection as parameters. It can merge two arrays but it returns a Set. So, we will have unique data but it will merge two arrays.

Way 3:

var mergedArraySize = array1.size + array2.size
var mergedArray = IntArray(mergedArraySize)
var pos = 0;
for (value in array1) {
    mergedArray[pos] = value
    pos++
}
for (value in array2) {
    mergedArray[pos] = value
    pos++
}
print(mergedArray.asList())

It will also print [1, 2, 3, 4, 5, 6].