PHP Array Functions

PHP ships with a large library of built-in functions that transform, filter, sort, and combine arrays without writing loops by hand.

Why use array functions?

Almost anything you might do to an array by writing a loop already has a well-tested built-in function. Reaching for these functions makes your code shorter, clearer, and usually faster, and it signals intent to other developers. This page covers the functions you will use most often, grouped by what they do.

Counting, searching, and testing

Finding what is in an array

<?php
$nums = [10, 20, 30, 40];

echo count($nums);              // 4
var_dump(in_array(30, $nums));  // bool(true)
echo array_search(40, $nums);   // 3 (the key)
var_dump(array_key_exists(2, $nums)); // bool(true)
?>

Note: in_array() and array_search() use loose comparison by default. Pass true as the third argument to require a strict type-and-value match, which avoids surprises like 0 matching the string "apple".

Transforming arrays

array_map() applies a function to every element and returns a new array of the results, while array_filter() keeps only the elements that pass a test. array_reduce() collapses a whole array down to a single value. None of these change the original array.

map, filter, and reduce

<?php
$numbers = [1, 2, 3, 4, 5];

$doubled = array_map(fn($n) => $n * 2, $numbers);
// [2, 4, 6, 8, 10]

$evens = array_filter($numbers, fn($n) => $n % 2 === 0);
// [1 => 2, 3 => 4]

$total = array_reduce($numbers, fn($carry, $n) => $carry + $n, 0);
// 15

print_r($doubled);
?>

Note: array_filter() preserves the original keys, so the result can have gaps. Wrap it in array_values() if you need a clean zero-based index afterwards.

Sorting arrays

PHP offers a family of sort functions that differ in whether they preserve keys and whether they sort by value or by key. All of them sort the array in place and return true on success rather than a new array.

Sorting values and keys

<?php
$scores = [3, 1, 2];
sort($scores);        // [1, 2, 3], keys reindexed

$ages = ["Ravi" => 30, "Mei" => 25];
asort($ages);         // sort by value, keep keys
ksort($ages);         // sort by key alphabetically

print_r($ages);
?>

Common array functions at a glance

Function	Purpose	Example result
count($a)	Number of elements	count([5,6,7]) is 3
in_array($v, $a)	True if a value exists	in_array(6, [5,6,7]) is true
array_keys($a)	Return all keys	keys of ["x"=>1] is ["x"]
array_values($a)	Reindex values 0..n	cleans gaps in keys
array_merge($a, $b)	Join two arrays	[1,2] + [3] is [1,2,3]
array_map($fn, $a)	Transform each element	double every number
array_filter($a, $fn)	Keep matching elements	keep only evens
sort($a)	Sort values ascending	[3,1,2] becomes [1,2,3]
array_slice($a, 1, 2)	Extract a sub-array	take 2 items from index 1
implode(",", $a)	Join to a string	[1,2] becomes "1,2"

array_merge() renumbers integer keys but overwrites duplicate string keys with the later value.
explode() and implode() convert between strings and arrays, which is handy for CSV-style data.
array_unique() removes duplicate values, and array_reverse() flips the order.
Most transforming functions return a new array, while most sorting functions modify in place.

Note: When you cannot remember exactly how a function orders its parameters, the official PHP manual entry for each function shows the signature and runnable examples. array_filter and array_map notably differ in argument order.

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