PHP array_unique() – Removing Duplicate Values from an Array

The article introduces the PHP array_unique() function, which takes an array and returns a new array with duplicate values removed while preserving original keys.

It explains that the function sorts values as strings, keeps the first occurrence of each value, and notes that key names remain unchanged. Optional sort_flags can modify sorting behavior using constants such as SORT_REGULAR , SORT_NUMERIC , SORT_STRING , and SORT_LOCALE_STRING .

Parameter details are provided: array – the input array, and sort_flags – optional flag to control sorting.

The function returns an array containing the unique values.

Example usage:

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

Output:

Array
(
    [green] => green
    [red]   => red
    [b]     => green
    [0]     => blue
)