How to find a key in an array by value in php

To determine the key of an array by knowing its value, there are at least three possible solutions:

1. You can use the well-known array_search function. We already used it earlier in the article on removing an element from an array.
2. Use a loop to iterate through all elements of the array and compare values to identify the key.
3. Use the array_walk function, imitating option 2.

Initial data:

<?php $array = [
    10 => 'Lorem',
    12 => 'Ipsum',
    15 => 'simply',
    20 => 'dummy',
    33 => 'text',
];

Above is an array where both keys and values are unique. Note: if your values are not unique, the returned key will be for the first matching element.

Example 1

Here we use PHP's array_search function to find the key of the value "simply":

<?php
//Example 1
$search_value = 'simply';
echo var_dump(array_search($search_value, $array));
echo "n";

The result will be — int(15)

Example 2

We use a foreach loop to go through the array and an if-statement to compare values:

<?php //Example 2
$search_value = 'Ipsum';
foreach( $array as $key => $value )
{
    if($search_value == $value)
    {
        var_dump($key);
        echo "\n";
        break;
    }
}

For the value "Ipsum", the result will be the key "int(12)"

Example 3

Probably the longest and weirdest method is using array_walk and passing the $search_key by reference through use:

<?php
//Example 3
$search_value = 'Lorem';
$search_key = NULL;
array_walk($array, function($value, $key, $search_value) use(&$search_key){
    if($search_value == $value)
    {
        $search_key = $key;
    }
}, $search_value);
var_dump($search_key);

The result will be either NULL (if not found), or int(10) if the value "Lorem" is found.

So, what’s the conclusion? Don’t overthink it — just use what’s already built into PHP, namely the ready-made array_search function.

Earlier, at the beginning of my PHP programming journey, I often wrote such "bicycles" like in examples 2 and 3. Over time, I got smarter and started checking the PHP docs to see if something already existed. And now, with platforms like GitHub, development speed can be increased even more. Good luck!