PHP Manual: Removes duplicate values from an array

Description

array array_unique(array $array, int $flags = SORT_STRING)

Takes an input array and returns a new array without duplicate values.

Note that keys are preserved. If multiple elements compare equal under the given flags, then the key and value of the first equal element will be retained.

Note: Two elements are considered equal if and only if (string) $elem1 === (string) $elem2 i.e. when the string representation is the same, the first element will be used.

Parameters

array

The input array.

flags

The optional second parameter flags may be used to modify the comparison behavior using these values:

Comparison type flags:

SORT_REGULAR - compare items normally (don't change types)
SORT_NUMERIC - compare items numerically
SORT_STRING - compare items as strings
SORT_LOCALE_STRING - compare items as strings, based on the current locale.

Return Values

Returns the filtered array.

Changelog

Version	Description
7.2.0	If `flags` is `SORT_STRING`, formerly `array` has been copied and non-unique elements have been removed (without packing the array afterwards), but now a new array is built by adding the unique elements. This can result in different numeric indexes.

Examples

Example #1 array_unique example

<?php
$input = array("a" => "green", "red", "b" => "green", "blue", "red");
$result = array_unique($input);
print_r($result);
?>

The above example will output:

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

Example #2 array_unique and types

<?php
$input = array(4, "4", "3", 4, 3, "3");
$result = array_unique($input);
var_dump($result);
?>

The above example will output:

array(2) {
  [0] => int(4)
  [2] => string(1) "3"
}

Notes

Note: Note that array_unique is not intended to work on multi dimensional arrays.

array_unique