PHP array_change_key_case Function

last modified March 13, 2025

The PHP array_change_key_case function changes the case of all keys in an array. It can convert keys to uppercase or lowercase.

Basic Definition

The array_change_key_case function returns an array with all keys converted to the specified case. It works with both string and numeric keys.

Syntax: array_change_key_case(array $array, int $case = CASE_LOWER): array. The $case parameter can be either CASE_LOWER or CASE_UPPER.

Basic array_change_key_case Example

This example demonstrates converting all array keys to lowercase.

basic_array_change_key_case.php

<?php

$user = [
    'FirstName' => 'John',
    'LastName' => 'Doe',
    'Age' => 30
];

$lowerKeys = array_change_key_case($user);

print_r($lowerKeys);

The output will show all keys converted to lowercase. Numeric keys remain unchanged as they're not affected by case conversion.

Converting to Uppercase

This example shows how to convert all keys to uppercase using the function.

uppercase_keys.php

<?php

$config = [
    'db_host' => 'localhost',
    'db_user' => 'admin',
    'db_pass' => 'secret'
];

$upperKeys = array_change_key_case($config, CASE_UPPER);

print_r($upperKeys);

The resulting array will have all keys in uppercase. This is useful when you need consistent key cases for case-sensitive operations.

Mixed Key Types

The function handles arrays with mixed key types (string and numeric).

mixed_keys.php

<?php

$mixed = [
    'Name' => 'Alice',
    0 => 'Zero',
    'Age' => 25,
    1 => 'One'
];

$lowerMixed = array_change_key_case($mixed);

print_r($lowerMixed);

Only string keys are converted to lowercase. Numeric keys remain unchanged in the output array, maintaining their original values and positions.

Duplicate Key Handling

When case conversion creates duplicate keys, later values overwrite earlier ones.

duplicate_keys.php

<?php

$data = [
    'USERNAME' => 'admin',
    'username' => 'guest',
    'Password' => '12345'
];

$uniformKeys = array_change_key_case($data);

print_r($uniformKeys);

Both 'USERNAME' and 'username' become 'username' after conversion. The last occurrence ('guest') overwrites the first value ('admin') in the result.

Multidimensional Arrays

The function only changes keys at the top level of the array structure.

multidimensional_array.php

<?php

$company = [
    'CompanyName' => 'ACME',
    'Departments' => [
        'Sales' => ['John', 'Jane'],
        'IT' => ['Mike', 'Sarah']
    ]
];

$lowerCompany = array_change_key_case($company);

print_r($lowerCompany);

Only the top-level keys ('CompanyName' and 'Departments') are converted. Nested array keys remain unchanged, preserving their original case.

Best Practices

Consistency: Use consistent key cases throughout your code.
Case Sensitivity: Be aware of case-sensitive operations.
Data Integrity: Check for potential key collisions.
Performance: Consider impact on large arrays.

Source

PHP array_change_key_case Documentation

This tutorial covered the PHP array_change_key_case function with practical examples showing its usage for array key case conversion.

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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