PHP array_intersect Function: How it Works with Examples

The PHP array_intersect function finds common values in arrays and returns matches as a new array.

Understand the array_intersect in PHP

The array_intersect function compares values from two or more arrays. It checks each element and returns a new array with the matched values.

The array_intersect function takes one main array and compares it with other arrays. It checks values one by one and builds a new array with only matches.

The syntax looks like this:

array_intersect($array1, $array2, ..$arrays)

• $array1 is the base array for comparison.
• $array2 is the second array to compare against.
• You can pass more arrays to extend the comparison.

The function scans values across arrays and builds a new array with matches.

Here is a quick example:

$first = [1, 2, 3, 4];
$second = [3, 4, 5, 6];

$result = array_intersect($first, $second);
print_r($result);

The function checks each number in both arrays. It finds 3 and 4 in both arrays. The final output contains these common values.

Here is the output:

Array
(
    [2] => 3
    [3] => 4
)

Use the array_intersect with an Associative Array

The function also works with associative arrays. It compares values only. It does not check keys in the comparison process.

For example:

$first = ["a" => "red", "b" => "green", "c" => "blue"];
$second = ["x" => "green", "y" => "yellow", "z" => "red"];

$result = array_intersect($first, $second);
print_r($result);

The function checks values in both arrays. It matches “red” and “green”. It returns them with keys from the first array.

Here is the output:

Array
(
    [a] => red
    [b] => green
)

Here is another example:

$first = ["k1" => "apple", "k2" => "mango", "k3" => "grape"];
$second = ["m1" => "apple", "m2" => "banana", "m3" => "grape"];
$third = ["p1" => "grape", "p2" => "apple", "p3" => "pear"];

$result = array_intersect($first, $second, $third);
print_r($result);

The function compares three arrays. It finds “apple” and “grape” in all arrays. It returns them with keys from the first array.

The output:

Array
(
    [k1] => apple
    [k3] => grape
)

The Difference Between array_intersect and Other PHP Array Functions

The array_intersect function checks values only. Other array functions may check keys or both keys and values.

• array_diff returns values from the first array that do not exist in other arrays.
• array_intersect_assoc compares both keys and values to find exact matches.
• array_diff_assoc compares both keys and values but returns only differences.

Here is a table that shows you the key differences

Use array_intersect to filter arrays by common values while and the array_diff when you want unmatched values. Use the *_assoc forms when keys also matter.

Examples of the array_intersect in PHP

Simple number match:

$one = [10, 20, 30, 40];
$two = [30, 40, 50, 60];

$result = array_intersect($one, $two);
print_r($result);

This shows how the function compares two numeric arrays and returns the matches. It scans both arrays and gives you [30, 40] as the final output:

Array
(
    [2] => 30
    [3] => 40
)

Mixed string values:

$first = ["dog", "cat", "rabbit"];
$second = ["cat", "lion", "dog"];
$third = ["horse", "dog", "cat"];

$result = array_intersect($first, $second, $third);
print_r($result);

This shows how the function compares three string arrays. It checks each value step by step and finds “dog” and “cat” as the common values.

Here is the output:

Array
(
    [0] => dog
    [1] => cat
)

Associative array use case:

$a1 = ["k1" => "pen", "k2" => "pencil", "k3" => "eraser"];
$a2 = ["x1" => "pencil", "x2" => "marker", "x3" => "pen"];

$result = array_intersect($a1, $a2);
print_r($result);

This shows how associative arrays return matched values with keys from the first array. It compares both arrays and finds “pen” and “pencil”. The output:

Array
(
    [k1] => pen
    [k2] => pencil
)

Advanced three-array match:

$alpha = ["red", "blue", "green", "yellow"];
$beta = ["green", "red", "purple"];
$gamma = ["red", "green", "black"];

$result = array_intersect($alpha, $beta, $gamma);
print_r($result);

This shows how three arrays return only values that exist in all. The function checks step by step and finds “red” and “green” as matches.

The output:

Array
(
    [0] => red
    [2] => green
)

Wrapping Up

You learned how the PHP array_intersect function works and how it compares values across arrays.

Here is a quick recap:

• The function checks common values across arrays.
• It works with both simple and associative arrays.
• It ignores keys and matches values only.
• The array_intersect differs from array_diff and *_assoc functions.
• It returns a new array with values that match.

FAQs

$a = [1, 2, 3, 4];
$b = [2, 4, 6];
$result = array_intersect($a, $b);
print_r($result);

Array
(
    [1] => 2
    [3] => 4
)

$a = ["id" => 101, "name" => "Ali"];
$b = ["user" => 500, "name" => "Ali"];
$result = array_intersect($a, $b);
print_r($result);

Array
(
    [name] => Ali
)

$a = [1, 2, 3, 4];
$b = [2, 4];
echo "Intersect:";
print_r(array_intersect($a, $b));

echo "Diff:";
print_r(array_diff($a, $b));

// Intersect:
Array
(
    [1] => 2
    [3] => 4
)

// Diff:
Array
(
    [0] => 1
    [2] => 3
)

$a = [1, 2, 3, 4];
$b = [2, 3];
$c = [3, 4, 5];
$result = array_intersect($a, $b, $c);
print_r($result);

Array
(
    [2] => 3
)

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