How to Change Array Key to Lowercase in PHP ?

Last Updated : 10 Jul, 2024

This article will show you how to change the array key case to lowercase using PHP. There are two approaches to changing the key case, these are:

Table of Content

Using array_change_key_case() function
Using foreach() and strtolower() functions
Using array_walk() with array_flip()
Using array_combine() and array_map() functions
Using array_reduce()

Using array_change_key_case() function

The array_change_key_case() function is used to change the case of all of the keys in a given array either to lower case or upper case. To change the key case to lowercase, we will add the value "CASE_LOWER".

Syntax:

array_change_key_case($arr, CASE_LOWER)

Example 1:

PHP

<?php 

// PHP Program to change the key 
// case to lovercase 
function change_case($arr) { 
    return array_change_key_case($arr, CASE_LOWER); 
} 

// Driver Code 
$arr = [ 
    "NAME" => "Akash", 
    "COMPANY" => "GFG", 
    "Address" => "Noida", 
    "Contact NO" => "+91-9876543210", 
]; 

print_r(change_case($arr)); 
?>

Output

Array
(
    [name] => Akash
    [company] => GFG
    [address] => Noida
    [contact no] => +91-9876543210
)

Using foreach() and strtolower() functions

In this approach, we will use foreach() loop to select each key one by one, and then use strtolower() function to convert the key to lowercase.

Example:

PHP

<?php 

// PHP Program to change the key 
// case to lovercase 
function change_case($arr) 
{ 
    foreach ($arr as $key => $val) { 
        echo strtolower($key) 
            . " => " . $val . "\n"; 
    } 
} 

// Driver Code 
$arr = [ 
    "NAME" => "Akash", 
    "COMPANY" => "GFG", 
    "Address" => "Noida", 
    "Contact NO" => "+91-9876543210", 
]; 

print_r(change_case($arr)); 
?>

Output

name => Akash
company => GFG
address => Noida
contact no => +91-9876543210

Using array_walk() with array_flip()

In PHP, array_walk() applies a callback function to each element of an array. When combined with array_flip(), it flips the keys and values of the array. This technique is useful for manipulating keys, such as changing them to lowercase or performing key-based operations efficiently.

Example:

PHP

<?php
$array = ["Name" => "John", "Age" => 30, "Country" => "USA"];

// Flip the array, then walk through it to perform operations on keys or values
array_walk(array_flip($array), function(&$value, $key) {
    // Modify the keys or values here
    $value = strtoupper($value); // Example: Convert values to uppercase
});

print_r($array);
?>

Output

Array
(
    [Name] => John
    [Age] => 30
    [Country] => USA
)

Using array_combine() and array_map() functions

In this approach, we first use array_keys() to extract the keys and array_map() with strtolower() to convert them to lowercase. Then, we use array_combine() to combine the new lowercase keys with the original values.

Example:

PHP

<?php
function change_key_case_lower($arr) {
    $lowercase_keys = array_map('strtolower', array_keys($arr));
    return array_combine($lowercase_keys, array_values($arr));
}

// Example usage:
$original_array = array("First" => 1, "Second" => 2, "Third" => 3);
$lowercase_array = change_key_case_lower($original_array);
print_r($lowercase_array);

?>

Output

Array
(
    [first] => 1
    [second] => 2
    [third] => 3
)

Using array_reduce()

array_reduce() can be used to iterate over the array and build a new array with lowercase keys.

Example: In this example we converts the keys of an associative array to lowercase using array_reduce and array_keys, and then prints the modified array