PHP array_unique() Function

The PHP array_unique() function removes duplicate values from an array, preserving the first occurrence of each value and reindexing the array with keys preserved. It's useful for filtering out redundant data and ensuring a collection of unique elements within an array.

Syntax

array array_unique($array , $sort_flags)

Note: The keys of the array are preserved. That is, the keys of the not-removed elements of the input array will be the same in the output array.

Parameters

: This function accepts two parameters out of which one is mandatory and the other is optional. Both of these parameters are described below:

1. $array: This parameter is mandatory to be supplied and it specifies the input array from which we want to remove duplicates.
2. $sort_flags: This is optional parameter. This parameter $sort_flags may be used to modify the sorting behavior using these values:
   • SORT_REGULAR: This is the default value of the parameter $sort_flags. This value tells the function to compare items normally (don't change types).
   • SORT_NUMERIC: This value tells the function to compare items numerically.
   • SORT_STRING: This value tells the function to compare items as strings.
   • SORT_LOCALE_STRING: This value tells the function to compare items as strings, based on the current locale.

Return Value: The array_unique() function returns the filtered array after removing all duplicates from the array.

Below programs illustrate the array_unique() function in PHP:

Example : In this example we removes duplicate values from the array a using array_unique() and prints the result.

<?php

// Input Array
$a=array("red", "green", "red", "blue");

// Array after removing duplicates
print_r(array_unique($a));

?>

Array
(
    [0] => red
    [1] => green
    [3] => blue
)

Example 2: In this example we removes duplicate values from the associative array arr using array_unique() and prints the result.

<?php

// Input array
$arr = array("a"=>"MH", "b"=>"JK", "c"=>"JK", "d"=>"OR");

// Array after removing duplicates
print_r(array_unique($arr));

?>

Array
(
    [a] => MH
    [b] => JK
    [d] => OR
)