PHP array_key_first Function: How it Works with Examples

The array_key_first helps you to get the first key of an array directly in PHP. It saves time and removes extra steps in your code.

What is the PHP array_key_first Function

PHP array_key_first gives the first key of an array. It works on indexed arrays and associative arrays. It returns null when the array is empty.

array_key_first(array $array)

This syntax shows that it takes one array and gives the first key or null.

The function looks at the array and reads the first key. It does not change the array and does not loop through every value.

Here is a quick example:

$items = ['apple', 'banana', 'cherry'];
$firstKey = array_key_first($items);
echo $firstKey; // 0

This code sets an array of items and then takes its first key. It prints the key of the first element.

PHP array_key_first with Indexed Arrays

This function reads the first index of a normal array and returns it. It works even when the array starts with a custom index number.

Here is an example:

$data = [5 => 'cat', 6 => 'dog', 7 => 'bird'];
echo array_key_first($data); // 5

The code sets an indexed array with custom keys and prints the first key.

PHP array_key_first with Associative Arrays

This function also works on associative arrays. It gives the first string key instead of a number key.

Here is an example:

$user = ['name' => 'Ali', 'age' => 30, 'city' => 'Jeddah'];
echo array_key_first($user); // name

The code sets an associative array with three keys and prints the first key.

PHP array_key_first vs array_keys Comparison

array_key_first gives the first key of an array directly. array_keys gives all keys of an array as a list.

Use array_key_first when you only need one key and the array_keys when you need every key.

Examples

Get First Key from Indexed Array:

$numbers = [10, 20, 30];
echo array_key_first($numbers); // 0

This example shows how to get the first key from a simple numeric array. It returns the key of the first value.

Get First Key from Associative Array:

$settings = ['theme' => 'dark', 'layout' => 'wide'];
echo array_key_first($settings); // theme

This example shows how to get the first key from an associative array. It returns the key of the first pair in that array.

Check Empty Array before Using array_key_first:

$data = [];
$key = array_key_first($data);
var_dump($key); // NULL

This example shows how the function returns null when the array has no values. You can check it before use.

Work with Mixed Keys:

$mix = [2 => 'x', 'b' => 'y', 3 => 'z'];
echo array_key_first($mix); // 2

This example shows how it handles mixed key types. It still gives the first key even if the array has numbers and strings.

Wrapping Up

You learned what PHP array_key_first does.

Here is a quick recap:

• It gives the first key of an array, and works on indexed or associative arrays.
• It returns null for empty arrays, and it differs from array_keys by returning only one key.

FAQs

$array = ["red" => 1, "blue" => 2, "green" => 3];
echo array_key_first($array); 

$array = [10, 20, 30, 40];
echo array_key_first($array);

$array = ["x" => 5, "y" => 6, "z" => 7];

print_r(array_key_first($array)); 
// Output: x

print_r(array_keys($array));
// Output: Array ( [0] => x [1] => y [2] => z )

$array = [];
var_dump(array_key_first($array));

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