How to convert array values to lowercase in PHP?

use array_map():

$yourArray = array_map('strtolower', $yourArray);

In case you need to lowercase nested array (by Yahya Uddin):

$yourArray = array_map('nestedLowercase', $yourArray);

function nestedLowercase($value) {
    if (is_array($value)) {
        return array_map('nestedLowercase', $value);
    }
    return strtolower($value);
}

Just for completeness: you may also use array_walk:

array_walk($yourArray, function(&$value)
{
  $value = strtolower($value);
});

From PHP docs:

If callback needs to be working with the actual values of the array, specify the first parameter of callback as a reference. Then, any changes made to those elements will be made in the original array itself.

Or directly via foreach loop using references:

foreach($yourArray as &$value)
  $value = strtolower($value);

Note that these two methods change the array "in place", whereas array_map creates and returns a copy of the array, which may not be desirable in case of very large arrays.

You could use array_map(), set the first parameter to 'strtolower' (including the quotes) and the second parameter to $lower_case_array.

If you wish to lowercase all values in an nested array, use the following code:

function nestedLowercase($value) {
    if (is_array($value)) {
        return array_map('nestedLowercase', $value);
    }
    return strtolower($value);
}

So:

[ 'A', 'B', ['C-1', 'C-2'], 'D']

would return:

[ 'a', 'b', ['c-1', 'c-2'], 'd']