How to Get All Keys of an Associative Array in PHP?

Last Updated : 16 Jul, 2024

Given an Associative array, the task is to get all the keys of the associative array in PHP. There are two approaches to get all keys from the associative array, these are - using array_keys(), and foreach loop. In this article, we will explore these approaches with examples.

Table of Content

Approach 1: Using the array_keys() Function
Approach 2: Using a foreach Loop
Approach 3: Using the array_walk() Function

Using the array_keys() Function

The array_keys() function returns an array containing the keys of an associative array.

PHP

<?php

$subjects = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

$keys = array_keys($subjects);

print_r($keys);

?>

Output

Array
(
    [0] => Maths
    [1] => Physics
    [2] => Chemistry
    [3] => English
    [4] => Computer
)

Using a foreach Loop

You can use a foreach loop to iterate over the associative array and extract the keys of array.

PHP

<?php

$subjects = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

$keys = [];

foreach ($subjects as $key => $value) {
    $keys[] = $key;
}

print_r($keys);

?>

Output

Array
(
    [0] => Maths
    [1] => Physics
    [2] => Chemistry
    [3] => English
    [4] => Computer
)

Using the array_walk() Function

The array_walk() function can be used to apply a callback function to each element of the array. We can use this to collect all the keys.

PHP

<?php

$subjects = array(
    "Maths" => 95, 
    "Physics" => 90,   
    "Chemistry" => 96, 
    "English" => 93,   
    "Computer" => 98
);

$keys = [];

array_walk($subjects, function($value, $key) use (&$keys) {
    $keys[] = $key;
});

print_r($keys);

?>

Output

Array
(
    [0] => Maths
    [1] => Physics
    [2] => Chemistry
    [3] => English
    [4] => Computer
)

Using array_map() Function

The array_map() function can be used to apply a callback function to the elements of an array. We can use this function to extract all the keys from an associative array by mapping the keys to a new array.

Example