Remove duplicated elements of associative array in PHP

In PHP, removing duplicated elements from associative arrays requires special handling since standard functions like array_unique() work only with simple values. For complex associative arrays, you need to serialize the arrays first, remove duplicates, then unserialize them back.

Syntax

The general approach combines array_map(), serialize(), array_unique(), and unserialize() functions −

array_map("unserialize", array_unique(array_map("serialize", $array)))

Example

Here's how to remove duplicate associative arrays from a multidimensional array −

<?php
$result = array(
    0 => array('a' => 1, 'b' => 'Hello'),
    1 => array('a' => 1, 'b' => 'duplicate_val'),
    2 => array('a' => 1, 'b' => 'duplicate_val'),
    3 => array('a' => 2, 'b' => 'World')
);

echo "Original array:<br>";
print_r($result);

$unique = array_map("unserialize", array_unique(array_map("serialize", $result)));

echo "\nArray after removing duplicates:<br>";
print_r($unique);
?>

Original array:
Array
(
    [0] => Array
        (
            [a] => 1
            [b] => Hello
        )

    [1] => Array
        (
            [a] => 1
            [b] => duplicate_val
        )

    [2] => Array
        (
            [a] => 1
            [b] => duplicate_val
        )

    [3] => Array
        (
            [a] => 2
            [b] => World
        )

)

Array after removing duplicates:
Array
(
    [0] => Array
        (
            [a] => 1
            [b] => Hello
        )

    [1] => Array
        (
            [a] => 1
            [b] => duplicate_val
        )

    [3] => Array
        (
            [a] => 2
            [b] => World
        )

)

How It Works

The process works in four steps:

• array_map("serialize", $result) − Converts each associative array to a string representation
• array_unique() − Removes duplicate string values
• array_map("unserialize", ...) − Converts the unique strings back to associative arrays
• Original array keys are preserved where duplicates are removed

Conclusion

This serialize/unserialize approach effectively removes duplicate associative arrays by converting them to comparable string representations. The method preserves original array structure while eliminating exact duplicates based on both keys and values.