CODEWITHSUNDEEP
arraysloopskotlinappend
sollarp
sollarp

Reputation: 21

Append List of array to an array and repeat this in kotlin

I can't seem to find a right solution. Trying to add a list of array to another array. With my Python background it is easily done but not in Kotlin.

val extra = arrayOf(7,7,7)

fun containerArray() {

    val even = arrayOf(2, 4, 6)

    val odd = arrayOf(1, 3, 5)

    val arr1 = arrayOf(even, odd)

    val arr2 = arrayOf(*arr1, extra)



    print(arr2.contentDeepToString())

 }

 fun main() {

     for (i in 1..3) {

        containerArray() 

    }

 }

When executing above code I receive...

[[2, 4, 6], [1, 3, 5], [7, 7, 7]][[2, 4, 6], [1, 3, 5], [7,7,7]][...
What I want to achieve is this ....

[ [2, 4, 6], [1, 3, 5], [7, 7, 7], [7, 7, 7], [7, 7, 7]]

Upvotes: 1

Views: 2423

Answers (3)

Sergio
Sergio

Reputation: 30625

I assume you want to get the following array:

[[2, 4, 6], [1, 3, 5], [7, 7, 7]]

There is an overridden + (plus) operator for Arrays in Kotlin, you can use it for adding arrays:

val arr2 = arr1 + extra

Resulting array arr2 will contain all elements of the original array arr1 and then all elements of the array extra.

ADDITIONALLY:

  • You can add another array to arr2:

    val anotherArray = arrayOf(5, 5, 5)
val arr3 = arr2 + anotherArray
// result: [[2, 4, 6], [1, 3, 5], [7, 7, 7], [5, 5, 5]]

  • If you want to use the same array arr2 to store elements, you can create it with var modifier:

    var arr2 = arr1 + extra
arr2 += arrayOf(5, 5, 5)

  • There are different ways of what you are trying to achieve using a loop, for example:

    val even = arrayOf(2, 4, 6)
val odd = arrayOf(1, 3, 5)
val extra = arrayOf(7,7,7)

var arr1 = arrayOf(even, odd)

for (i in 1..3) {
    arr1 += extra
}

arr1 will contain next elements: [[2, 4, 6], [1, 3, 5], [7, 7, 7], [7, 7, 7], [7, 7, 7]]

Upvotes: 3

cactustictacs
cactustictacs

Reputation: 19524

Do you get why you're getting that result? arrayOf(items) creates a new array wrapping those items, so arrayOf(even, odd) is an array that contains two arrays. Then you create another array, containing that array-of-arrays and another single array. You're nesting them as you go

Sweeper's answer is probably what you want, but there are a lot of ways to combine collections, flatten sequences etc. Like one thing you can do is use the *operator (the "spread operator") to "unpack" your arrays, so you get the items instead:

   // unpack arr1 from an array of arrays, into just those arrays
   // equivalent to arrayOf([2, 4, 6], [1, 3, 5], extra)
   val arr2 = arrayOf(*arr1, extra)

   print(arr2.contentDeepToString())
   >> [[2, 4, 6], [1, 3, 5], [7, 7, 7]]

There's also flatMap, flatten etc - the best option depends on what you're doing!

Also when you say you want this:

[2, 4, 6], [1, 3, 5], [7, 7, 7]

that's just a bunch of values, not contained in anything, so we're assuming you want this:

[[2, 4, 6], [1, 3, 5], [7, 7, 7]]

where they're held in an array (or it could be a list). You could use the spread operator to unpack that into a bunch of values, but all you can do with that is pass it as a variable number of arguments to a function (which is what's happening in arrayOf)

Upvotes: 2

Sweeper
Sweeper

Reputation: 270980

To add a thing to an array of things, and produce a new array, use plusElement:

val arr2 = arr1.plusElement(extra)

This not only works for arrays, but also works for any Iterables, i.e. Lists, Sets etc.

Upvotes: 2

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