How to copy a two-dimensional array in Kotlin?

Question

This method works fine. However, I think it is not functional.

fun getCopy(array: Array<BooleanArray>): Array<BooleanArray> {
    val copy = Array(array.size) { BooleanArray(array[0].size) { false } }
    for (i in array.indices) {
        for (j in array[i].indices) {
            copy[i][j] = array[i][j]
        }
    }
    return copy
}

Is there a more functional way?

miensol · Accepted Answer · 2016-11-07 12:57:58Z

19

You can make use of clone like so:

fun Array<BooleanArray>.copy() = map { it.clone() }.toTypedArray()

or if you'd like to save some allocations:

fun Array<BooleanArray>.copy() = arrayOfNulls<ByteArray>(size).let { copy ->
    forEachIndexed { i, bytes -> copy[i] = bytes.clone() }
    copy
} as Array<BooleanArray>

or even more concise as suggested by @hotkey:

fun Array<BooleanArray>.copy() = Array(size) { get(it).clone() }

edited Nov 7, 2016 at 12:57

answered Nov 7, 2016 at 11:07

miensol

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1 Comment

hotkey Over a year ago

Another allocation-efficient implementation: fun Array<BooleanArray>.copy() = Array(size) { get(it).clone() }

mxcoder · Accepted Answer · 2018-02-18 12:02:10Z

-1

What about using copyOf()?

val copyOfArray = array.copyOf()

Returns new array which is a copy of the original array

Reference here

answered Feb 18, 2018 at 12:02

mxcoder

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2 Comments

hoijui Over a year ago

the sample code in the question indicates that a deep copy is required. this code creates a shallow copy.

Moaz Rashad Over a year ago

This keeps references of internal array

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