1

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]]
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3 Answers 3

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3

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]]

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8 Comments

What result do you want to get and are getting using + operator? This should work and the result array should be [[2, 4, 6], [1, 3, 5], [7, 7, 7]]. I guess you wrongly described the result you want to get in your question then.
Sergey and @ cactustictacs absolutely right. The code example works but if I try to add and other array to arr2 using loop it just replacing the last element of the array. I have not tried the mutableList but I think it is the right approach in this case. So this is the result I looking for [[2, 4, 6], [1, 3, 5], [7, 7, 7]] and after my loop add an extra element to the list like [[2, 4, 6], [1, 3, 5], [7, 7, 7], [5,5,5]] and so for on.
@PSoll I've added some additional information to my answer. I don't quite understand how you try to add elements in the loop, it would be nice to see some example (you can edit your question).
find a code here: play.kotlinlang.org/…
so you are calling containerArray() three times, and it prints the same result every time. What are you trying to achieve?
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2

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.

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Comments

2

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)

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3 Comments

Guys Thanks for your advise. Both the answers are added to my knowledge. # cactustictacs to your question yes I want to achieve a nested array [[2, 4, 6], [1, 3, 5], [7, 7, 7]] and than use and index to select a list of array. However in my scenario I'm using a for loop to add a new list to this array which does not work as I excpected.
@PSoll If you have your container array (the outer one) and the item arrays (the [2, 4, 6] etc), then you need to create your container, maybe starting with a couple of items included - arrayOf() or arrayOf(even, odd). Then just adding item arrays (using one of the plus methods in the other answers) is the easiest way to do it. arr1 += extra works!
@PSoll One thing to watch out for is that Kotlin encourages immutable collections, so there are lots of functions that don't change the original, they create a new copy with the changes, and return that. plusElement is one, so arr1.plusElement(extra) won't change arr1, it just produces a copy with the addition. That's necessary for arrays anyway - they're fixed length, if you want to "add" to one you need to create a new array and assign it to the variable. You'd generally use a mutableList instead - you can call toTypedArray() at the end if you really want an array for some reason

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