CODEWITHSUNDEEP
javakotlin
Dishonered
Dishonered

Reputation: 8851

Kotlin - Create an ArrayList of random Integers of specified length?

I have an ArrayList like this :

var amplititudes : ArrayList<Int> = ArrayList()

I want to populate this with random Ints. How can I do this?

Upvotes: 14

Views: 16154

Answers (7)

nakhodkin
nakhodkin

Reputation: 1465

import kotlin.random.Random


fun main() {
    // creates an instance of ArrayList<Int!>
    val list = ArrayList(List(10) { Random.nextInt() })
}

Verified on Kotlin v2.0.20

Upvotes: 0

Willi Mentzel
Willi Mentzel

Reputation: 29864

Since Kotlin 1.3 was released there is no need to use Java's java.util.Random which would restrict your code to the JVM. Instead kotlin.random.Random was introduced which is available on all platforms that support Kotlin.

val amplititudes  = IntArray(10) { Random.nextInt() }.asList()

Since you work with a companion object, you don't need to worry about instanting a Random object each iteration (like it was with the Java one that you would have had to put in a variable).

Upvotes: 5

Md Johirul Islam
Md Johirul Islam

Reputation: 5162

One option is to use the array constructor as following:

var amplititudes  = IntArray(10) { Random().nextInt() }.asList()

Another strategy is:

var amplititudes  = (1..10).map { Random().nextInt() }

EDIT (OUTDATED!)

You no longer need to do this, as Kotlin will only create a single instance of Random.

As suggested in the comment instead of creating an instance of Random each time it is better to initialize it once:

var ran = Random()
var amplititudes  = (1..10).map { ran.nextInt() }

Upvotes: 21

Youcef LAIDANI
Youcef LAIDANI

Reputation: 60046

Based to the answer of @Md Johirul Islam You can also use :

val from = 0
val to = 11
val random = Random
var amplititudes  = IntArray(10) { random.nextInt(to - from) +  from }.asList()

in this solution you can specify the range of ints that you want, from 0 to 10 for example

Upvotes: 6

AndrewBloom
AndrewBloom

Reputation: 2438

At this time, is not specified in your question the range of the Ints and how many do you need.

So I restrict the case to [n,m] interval, and I suppose you want all the m-n+1 elements.

Taking advantage of method shuffle of ArrayList, 

var shuffledList = ArrayList((n..m).toList())
shuffledList.shuffle()

Upvotes: 0

Mickey Mouse
Mickey Mouse

Reputation: 55

To generate a random number of specified length of List and between certain limits, use:

val rnds = (1..10).map { (0..130).random() }

Where (1..0) -> return list of 10 items (0..130) -> return random number between given range

Upvotes: 1

s1m0nw1
s1m0nw1

Reputation: 82027

Maybe something like this:

val amplitudes = ThreadLocalRandom.current().let { rnd ->
    IntArray(5) { rnd.nextInt() }
}

Or this:

val amplitudes = ThreadLocalRandom.current().let { rnd ->
    (0..5).map { rnd.nextInt() }.toIntArray()
}

Upvotes: 4

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