PHP array_search(): Find the Key of a Value

array_search($value, $array) returns the key of the first element equal to $value, or false if no element matches. Because a found key can be 0, test the result with !== false, as in if (($key = array_search('pear', $fruits)) !== false).

<?php
$fruits = ['apple', 'pear', 'plum'];

$key = array_search('pear', $fruits);
var_dump($key);

$key = array_search('kiwi', $fruits);
var_dump($key);

$prices = ['apple' => 1.20, 'pear' => 0.90];
echo array_search(0.90, $prices), "\n";   // works with string keys too

If you only need a yes or no, in_array() says so directly. array_search() is for when you need to know where the value sits, for example to change or remove it.

The 0 vs false pitfall

The most common array_search() bug: the value is the first element, its key is 0, and if ($key) treats 0 as false. The code says "not found" for a value that is right there. Compare with !== false, which only matches a real false.

<?php
$queue = ['Ada', 'Linus', 'Grace'];

if (array_search('Ada', $queue)) {
    echo "Wrong check: found\n";
} else {
    echo "Wrong check: not found\n";      // this runs, key is 0
}

$key = array_search('Ada', $queue);
if ($key !== false) {
    echo "Right check: found at $key\n";
}

!= false has the same bug as if ($key), because 0 == false is true. Only the strict operator tells them apart.

Strict search

Like in_array(), array_search() compares with == unless you pass true as the third argument. Loose mode lets a string find a number and null find 0, which returns a key you did not expect.

<?php
$ids = [10, 20, 30];
var_dump(array_search('20', $ids));         // loose: "20" == 20
var_dump(array_search('20', $ids, true));   // strict: no match

$stock = ['apples' => 5, 'pears' => 0];
var_dump(array_search(null, $stock));       // null == 0: finds 'pears'
var_dump(array_search(null, $stock, true));

Find all keys with a value

array_search() stops at the first match. array_keys($array, $value) returns every matching key as an array; add true for a strict comparison. An empty result means no match, so there is no 0 vs false confusion.

<?php
$seats = ['A1' => 'free', 'A2' => 'taken', 'A3' => 'free', 'A4' => 'taken'];

echo array_search('free', $seats), "\n";          // first only
print_r(array_keys($seats, 'free', true));       // all of them

$colors = ['red', 'blue', 'red', 'green', 'red'];
echo implode(', ', array_keys($colors, 'red')), "\n";

Search a multidimensional array with array_column

array_search() does not look inside nested arrays. For a list of rows, extract the field you are searching with array_column(); the positions in that list match the row numbers, so the result is the index of the row.

<?php
$users = [
    ['id' => 101, 'name' => 'Ada',   'email' => 'ada@example.com'],
    ['id' => 102, 'name' => 'Linus', 'email' => 'linus@example.com'],
    ['id' => 103, 'name' => 'Grace', 'email' => 'grace@example.com'],
];

$i = array_search('linus@example.com', array_column($users, 'email'), true);
if ($i !== false) {
    echo "Found {$users[$i]['name']} with id {$users[$i]['id']}\n";
}

// When rows are looked up often, index them once by the field instead
$byEmail = array_column($users, null, 'email');
echo $byEmail['grace@example.com']['id'], "\n";

array_column() renumbers its output from 0, so this only lines up when the rows are numbered 0, 1, 2 without gaps. After unset() or array_filter() the numbering has gaps; run array_values() on the rows first or use the keyed lookup in the last two lines. array_column() has more on the index-key form.

Case-insensitive search

array_search() compares strings exactly. Lowercase both sides to ignore case. array_map() keeps the keys, so the key you get back is the key in the original array.

<?php
$tags = ['first' => 'PHP', 'second' => 'Laravel', 'third' => 'MySQL'];

var_dump(array_search('mysql', $tags, true));

$lower = array_map('strtolower', $tags);
$key = array_search(strtolower('mysql'), $lower, true);
var_dump($key);
echo $tags[$key], "\n";

Search and replace or remove

The usual reason to search is to act on the element you found. With the key in hand, assign to change it or unset() to remove it, and always guard with !== false first: unset($arr[false]) silently removes the element with key 0.

<?php
$todo = ['buy milk', 'call Ada', 'write report'];

$key = array_search('call Ada', $todo, true);
if ($key !== false) {
    $todo[$key] = 'call Ada (done)';
}

$key = array_search('buy milk', $todo, true);
if ($key !== false) {
    unset($todo[$key]);
}

$todo = array_values($todo);   // renumber after unset
print_r($todo);