PHP array_intersect Function

last modified March 13, 2025

The PHP array_intersect function compares arrays and returns values present in all arrays. It's useful for finding common elements.

Basic Definition

The array_intersect function computes the intersection of arrays. It returns an array containing all values present in all input arrays.

Syntax: array_intersect(array $array1, array $array2, ...): array. Keys are preserved from the first array. Comparison is done using loose typing.

Basic array_intersect Example

This shows finding common numbers between two simple arrays.

basic_array_intersect.php

<?php

$array1 = [1, 2, 3, 4, 5];
$array2 = [3, 4, 5, 6, 7];

$result = array_intersect($array1, $array2);

print_r($result);

This finds numbers present in both arrays. The result contains 3, 4, and 5 with their original keys from the first array preserved.

String Value Intersection

Find common string values between multiple arrays.

string_intersection.php

<?php

$colors1 = ["red", "green", "blue"];
$colors2 = ["green", "blue", "yellow"];
$colors3 = ["blue", "purple", "green"];

$commonColors = array_intersect($colors1, $colors2, $colors3);

print_r($commonColors);

This finds colors present in all three arrays. Only "green" and "blue" appear in all input arrays, so they are returned with their original keys.

Associative Array Intersection

Find common values in associative arrays while preserving keys.

associative_intersect.php

<?php

$users1 = [
    "admin" => "Alice",
    "editor" => "Bob",
    "viewer" => "Charlie"
];

$users2 = [
    "manager" => "Alice",
    "editor" => "Bob",
    "guest" => "Dave"
];

$commonUsers = array_intersect($users1, $users2);

print_r($commonUsers);

This finds common values in associative arrays. The keys from the first array are preserved in the result, showing Alice and Bob are common to both arrays.

Mixed Type Comparison

Demonstrate how array_intersect handles different types with loose comparison.

mixed_types.php

<?php

$array1 = [1, "2", 3, "4", true];
$array2 = ["1", 2, "3", 4, false];

$result = array_intersect($array1, $array2);

print_r($result);

This shows loose type comparison. The string "1" equals integer 1, and "3" equals 3, so these values are included in the result despite type differences.

Multiple Array Intersection

Find common elements across more than two arrays.

multiple_arrays.php

<?php

$array1 = [10, 20, 30, 40, 50];
$array2 = [20, 30, 50, 60];
$array3 = [10, 20, 30, 70];
$array4 = [20, 30, 80, 90];

$common = array_intersect($array1, $array2, $array3, $array4);

print_r($common);

This finds values present in all four arrays. Only 20 and 30 appear in every input array, so they are returned with their original keys from the first array.

Best Practices

Type Awareness: Be mindful of loose comparison behavior.
Key Preservation: Remember keys come from first array.
Performance: For large arrays, consider sorting first.
Strict Comparison: Use array_uintersect for strict checks.

Source

PHP array_intersect Documentation

This tutorial covered the PHP array_intersect function with practical examples showing its usage for finding common array elements.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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