PHP array_find_key: How it Works with Examples

The PHP array_find_key function finds a key in an array by a condition. It checks each element and returns the first key that matches.

Understand the array_find_key in PHP

The array_find_key function returns the first key that matches a callback test. It scans each element in order and stops at the first match. This function was released in PHP 8.4.

The syntax looks like this:

array_find_key(array $array, callable $callback)

• $array is the input array.
• $callback is the function that checks each value.
• It returns the matching key or false if no key matches.

The function takes an array and a test. It checks each element. Once the callback returns true, it gives back the key. If no element passes, it returns false.

Here is a quick example:

$arr = ["a" => 2, "b" => 7, "c" => 10];
$key = array_find_key($arr, fn($v) => $v > 5);
echo $key; // b

The function checks each value. It finds 7 at key "b". The result is "b".

The Difference Between array_find_key and array_search

This array_find_key runs a test on each value with a callback. It stops once the test returns true. It then gives back the key.

The array_search looks for a direct value in the array. It does not use a test. It compares values and returns the first matching key.

Here are the key differences:

Use array_find_key if you need a test like greater than or less than. Use array_search if you need a direct match of a value.

Examples of array_find_key in PHP

Find the first number over a limit:

$nums = [3, 6, 9, 12, 15];
$key = array_find_key($nums, fn($v) => $v > 10);
echo $key; // 3

The function scans the list from left to right. It stops once it finds 12. The output key is 3 since the value 12 sits at that index.

Find the first word that starts with the letter:

$words = ["cat", "dog", "bird", "ant"];
$key = array_find_key($words, fn($v) => $v[0] === "b");
echo $key; //2

The test checks the first letter of each word. It finds "bird" as the first match. The index of "bird" is 2 and that is the result.

Find the first user with an age above 18:

$users = [
   ["name" => "Ali", "age" => 15],
   ["name" => "Sara", "age" => 20],
   ["name" => "Omar", "age" => 25]
];
$key = array_find_key($users, fn($v) => $v["age"] > 18);
echo $key; // 1

The test checks each age in the list. It finds "Sara" since her age is 20. The function then stops and returns the key 1.

Find the first product with a price under the limit:

$products = [
   "apple" => 5,
   "banana" => 8,
   "mango" => 12,
   "grape" => 15
];
$key = array_find_key($products, fn($v) => $v < 10);
echo $key; // apple

The test checks each price in the list. The first match is "apple" with value 5. The function then returns the key "apple".

Wrapping Up

You learned the use of array_find_key and the way it differs from array_search. Here is a quick recap:

• The array_find_key gives you the ability to run a test with a callback.
• It returns the first key that passes the test.
• The array_search looks for a direct value without a test.
• You can use the array_find_key to check and array_search for direct value matches.

FAQs

$array = ["id" => 101, "name" => "Ali", "age" => 22];
$key = array_search("Ali", $array);
echo $key; // Output: name

$data = ["red" => 1, "blue" => 2, "green" => 3];
$key = array_search(2, $data);
echo $key; // Output: blue

$array = [
    "user1" => ["id" => 101, "name" => "Sara"],
    "user2" => ["id" => 102, "name" => "Omar"]
];

foreach ($array as $key => $value) {
    if ($value["name"] === "Omar") {
        echo $key; // Output: user2
    }
}

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

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