PHP array_change_key_case() Function

In this tutorial, we will learn how we can convert all the keys of an input array to uppercase or lowercase by using the array_change_key_case() function.
Captain Salem 2 min read
PHP array_change_key_case() Function


In PHP, an array is a type of data structure that can hold multiple values or elements under a single variable name. These values can be of any data type such as string, integer, float, or even another array. Each value in an array is identified by a unique index or key, which can be a number or a string.

We can create an array in PHP using various methods and techniques such as the array() function, square bracket [] notation and more. Check the tutorial below to learn more.

PHP Array() Function
In this tutorial, we will explore how we can use the array() method in PHP to create an index array and assign elements to it.

Function Syntax

The following shows the definition for the array_change_key_case() method.

array_change_key_case(array $array, int $case = CASE_LOWER): array

Function Parameters

The function accepts two main parameters:

  1. array - this refers to the input array on which the function will operate.
  2. case - Defines the casing to which the key is converted. Accepted values are
  3. CASE_UPPER - Convert to Uppercase
  4. CASE_LOWER - Convert to Lowercase.

Function Return Value

The function returns an array with all the keys converted to lower case or uppercase. If the input value is not a valid array, the function will return null.


Let us look at some basic examples of the function usage.

Example 1

The following example demonstrates how to use the function to convert all the keys of an input array to uppercase.

$databases = array(
  "mysql" => 3306,
  "postgresql" => 5432,
  "redis" => 6379,
  "sql server" => 1433

$databases_uppercase = array_change_key_case($databases, CASE_UPPER);


In this case, we use the array_change_key_case() method to convert the keys of the array to uppercase, and store the result in a new array called $databases_uppercase.

Resulting output:

    [MYSQL] => 3306
    [POSTGRESQL] => 5432
    [REDIS] => 6379
    [SQL SERVER] => 1433

Example 3

Similarly, we can use this function to convert the keys of an input array to lowercase. An example is as shown:

$databases = array(
  "MYSQL" => 3306,
  "POSTGRESQL" => 5432,
  "REDIS" => 6379,
  "SQL SERVER" => 1433

$databases_lowercase = array_change_key_case($databases, CASE_LOWER);


The resulting output is as shown:

    [mysql] => 3306
    [postgresql] => 5432
    [redis] => 6379
    [sql server] => 1433


In this tutorial, we learned how we can use the array_change_key_case() method to convert the keys of an input array to either lower case or uppercase.

We hope you enjoyed this post.

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