How to remove duplicates from an array Kotlin with example

How to remove duplicates from an array Kotlin with example

This tutorial explains multiple ways to remove duplicate elements

The first way to use the distinct() function is to return an array of unique elements and elements in insertion order. The second way using toSet(), returns a Set of elements and order is not preserved. The third way using toMutableSet(), returns the MutableSet of elements and order is preserved. The second way using toHashSet(), returns HashSet of elements and order is not preserved

Array finds unique elements

There are multiple ways to remove duplicate elements from an array.

  • using disticnt array function distinct() function removes an duplicate elements. Elements can be strings or any type and return unique elements.

The size of the original is always not the same as the result array if there are duplicate elements.

It returns an Array type and the result array order is preserved

here is an example

import java.util.Arrays

fun main() {
    val numbers: Array<Int> = arrayOf(11, 11,12, 13, 14, 15,11)
    println(Arrays.toString(numbers)) // [11, 11, 12, 13, 14, 15, 11]

    println(numbers.distinct())// [11, 12, 13, 14, 15]

}
  • toSet function

toSet function converts the array to Set and Set is a Data structure that does not allow to save duplicate elements by design.

Result array elements are not ordered, It always returns Set, not Array

import java.util.Arrays

fun main() {
    val numbers: Array<Int> = arrayOf(11, 11,12, 13, 14, 15,11)
    println(Arrays.toString(numbers))
    println(numbers.toSet())

}
  • using the toMutableSet function

Another way to return unique elements. It converts the MutableSet type and stores unique elements. The return type is MutableSet.

Result Set stores elements in Ordered due to the implementation of LinkedHashSet

import java.util.Arrays

fun main() {
    val strs: Array<String> = arrayOf("one","two","one","three")
    println(Arrays.toString(strs)) // [one, two, one, three]
    println(strs.toMutableSet()) //[one, two, three]

}
  • using the toHashSet function

It converts the HashSet type and stores unique elements. The return type is HashSet.

import java.util.Arrays

fun main() {
    val strs: Array<String> = arrayOf("one","two","one","three")
    println(Arrays.toString(strs))
    println(strs.toHashSet())

}

Conclusion

Multiple approaches are used to remove duplicate elements from an array.

use the distinct() function, If you want to return an element to an Array.

use toSet() function, if the result type expected is Set.