PHP array_intersect_key() Function
Quick summary: The PHP array_intersect_key() function returns all elements from the first array whose keys are present in all other arrays.
PHP array_intersect_key() Syntax
array_intersect_key(array $array, array ...$arrays): arrayPHP
PHP array_intersect_key() Basic examples
$a = ['a'=>1,'b'=>2,'c'=>3];
$b = ['a'=>9,'c'=>8];
print_r(array_intersect_key($a, $b));PHP
Output:
Array ( [a] => 1 [c] => 3 )Returns elements whose keys exist in both arrays.
PHP array_intersect_key() Real-world usage
$input = ['name'=>'John','email'=>'john@example.com','role'=>'admin'];
$allowed = ['name'=>true,'email'=>true];
print_r(array_intersect_key($input, $allowed));PHP
Output:
Array ( [name] => John [email] => john@example.com )Whitelist filtering of user input.
PHP array_intersect_key() Edge cases
$a = ['1'=>'x'];
$b = [1=>'y'];
print_r(array_intersect_key($a, $b));PHP
Output:
Array ( [1] => x )String and integer keys may be treated as identical.
PHP array_intersect_key() Common mistakes
Expecting value comparison
array_intersect_key() compares only keys.
Incorrect
array_intersect_key(['a'=>1], ['a'=>2]);Correct
array_intersect_assoc(['a'=>1], ['a'=>2]);Use array_intersect_assoc() if values must also match.
PHP array_intersect_key() Frequently Asked Questions
What does array_intersect_key() do?
Computes intersection using keys only.
Use case?
Filtering by keys.
Ignores values?
Yes.
Return type?
Array.
Common mistake?
Expecting value comparison.
Performance?
Fast.
Safe?
Yes.
Alternative?
array_diff_key().
Handles nested arrays?
No.
Case sensitive?
Yes.
Best practice?
Normalize keys.
Used in configs?
Yes.