Merge two or more arrays in Kotlin

This article explores different ways to merge multiple arrays in Kotlin into a single array. The solution should maintain the original order of elements in individual arrays.

1. Using Plus Operator

A simple and fairly efficient solution to combine two arrays in Kotlin is with the plus operator. This is demonstrated below:

inline fun<reified T> merge(vararg arrays: Array<T>): Array<T?> {

var result: Array<T?> = arrayOfNulls(0);

for (array in arrays) {

result += array;

}

return result

}

fun main() {

val first: Array<String> = arrayOf("A", "B")

val second: Array<String> = arrayOf("C", "D")

val third: Array<String> = arrayOf("E", "F")

val result = merge(first, second, third)

println(result.contentToString()) // [A, B, C, D, E, F]

}

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An equivalent way is to use the plus() function.

inline fun<reified T> merge(vararg arrays: Array<T>): Array<T?> {

var result: Array<T?> = arrayOfNulls(0);

for (array in arrays) {

result = result.plus(array);

}

return result

}

2. Using `copyOf()` with `System.arraycopy()` function

The idea is to allocate enough memory to the new array for accommodating all elements present in all arrays using the copyOf() function. Then use System.arraycopy() to copy the given arrays into the new array, as shown below:

fun <T> merge(vararg arrays: Array<T>): Array<T?>? {

var totalSize = 0

for (array in arrays) {

totalSize += array.size

}

var dest: Array<T?>? = null

var destPos = 0

for (array in arrays)

{

if (dest == null)

{

dest = array.copyOf(totalSize)

destPos = array.size

}

else {

System.arraycopy(array, 0, dest, destPos, array.size)

destPos += array.size

}

return dest

}

fun main() {

val first: Array<String> = arrayOf("A", "B")

val second: Array<String> = arrayOf("C", "D")

val third: Array<String> = arrayOf("E", "F")

val result = merge(first, second, third)

println(result?.contentToString()) // [A, B, C, D, E, F]

}

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3. Using `MutableList`

We can also use a MutableList to merge multiple arrays in Kotlin, as shown below. This approach uses the addAll() function:

inline fun<reified T> merge(vararg arrays: Array<T>): Array<T> {

val list: MutableList<T> = ArrayList()

for (array in arrays) {

list.addAll(array.map { i -> i })

}

return list.toTypedArray()

}

fun main() {

val first: Array<String> = arrayOf("A", "B")

val second: Array<String> = arrayOf("C", "D")

val third: Array<String> = arrayOf("E", "F")

val result = merge(first, second, third)

println(result.contentToString()) // [A, B, C, D, E, F]

}

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That’s all about merging multiple arrays in Kotlin.

Merge two or more arrays in Kotlin

1. Using Plus Operator

2. Using copyOf() with System.arraycopy() function

3. Using MutableList

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2. Using `copyOf()` with `System.arraycopy()` function

3. Using `MutableList`