Array Functions

PHP includes more than 80 built-in array functions. Knowing which ones exist — and which one fits a task — lets you replace many hand-written loops with a single, well-tested function call. This lesson is a categorized reference with examples for functions not covered in detail in earlier lessons, plus a few rules that apply to all of them.

General Rules

1. Most functions return a new array and leave the input unchanged: array_map(), array_filter(), array_merge(), array_slice(), array_reverse(), and others.
2. Some functions modify the array in place (they take it by reference) and return something else: all sort functions, array_push(), array_pop(), array_shift(), array_unshift(), array_splice(), shuffle(), array_walk().
3. Key handling differs: some functions preserve keys (array_filter(), asort(), array_slice() for string keys), others re-index (sort(), array_values(), array_merge() for integer keys). Check the manual when keys matter.
4. Comparison mode: search functions compare loosely unless you pass true for strict mode (in_array(), array_search(), array_keys()).

Reference by Category

Inspecting

Keys and Values

Adding, Removing, Extracting

Combining and Comparing

Transforming

Searching

Sorting

sort(), rsort(), asort(), arsort(), ksort(), krsort(), usort(), uasort(), uksort(), natsort(), natcasesort(), array_multisort(), shuffle() — see Sorting Arrays.

Calculating

Generating

Selected Functions in Detail

array_chunk() — Split Into Groups

<?php
print_r(array_chunk(range(1, 7), 3));

Output

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )
    [1] => Array
        (
            [0] => 4
            [1] => 5
            [2] => 6
        )
    [2] => Array
        (
            [0] => 7
        )
)

The last chunk may be smaller. Passing true as the third argument preserves the original keys. Typical uses: paginating results, building grid rows (three products per row), and sending data to an API in batches.

array_count_values() — Count Occurrences

<?php
$votes = ['php', 'js', 'php', 'go', 'php', 'js'];
$counts = array_count_values($votes);
arsort($counts);
print_r($counts);

Output

Array
(
    [php] => 3
    [js] => 2
    [go] => 1
)

Values become keys, and counts become values. It works for strings and integers.

array_flip() — Swap Keys and Values

<?php
$codes = ['IN' => 'India', 'JP' => 'Japan'];
print_r(array_flip($codes));

Output

Array
(
    [India] => IN
    [Japan] => JP
)

Use it to create reverse lookups or to turn a list into a set for fast isset() checks. Duplicate values collapse into one key (the last one wins).

array_intersect() and array_diff() — Set Operations

<?php
$required = ['php', 'mysql', 'git', 'linux'];
$candidate = ['php', 'git', 'docker'];
$matching = array_values(array_intersect($required, $candidate));
$missing = array_values(array_diff($required, $candidate));
echo "Matching skills: " . implode(', ', $matching) . "\n";
echo "Missing skills: " . implode(', ', $missing) . "\n";

Output

Matching skills: php, git
Missing skills: mysql, linux

Both functions preserve the keys of the first array, so array_values() re-indexes the results. The _key and _assoc variants compare keys or key–value pairs instead of values.

array_slice() — Extract a Portion

<?php
$leaderboard = ['Charu', 'Asha', 'Dev', 'Bala', 'Esha'];
echo "Top 3: " . implode(', ', array_slice($leaderboard, 0, 3)) . "\n";
echo "Last 2: " . implode(', ', array_slice($leaderboard, -2)) . "\n";
echo "Original count: " . count($leaderboard) . "\n";

Output

Top 3: Charu, Asha, Dev
Last 2: Bala, Esha
Original count: 5

Unlike array_splice(), array_slice() does not modify the original array.

array_walk_recursive() — Apply a Callback to Every Leaf Value

<?php
$formData = [
    'name' => '  Asha ',
    'address' => ['city' => ' Chennai ', 'pin' => ' 600042 '],
];
array_walk_recursive($formData, function (mixed &$value): void {
    if (is_string($value)) {
        $value = trim($value);
    }
});
echo json_encode($formData) . "\n";

Output

{"name":"Asha","address":{"city":"Chennai","pin":"600042"}}

array_walk_recursive() visits every non-array value at any depth. The callback receives each value by reference (&$value), so it can modify the array in place — here, trimming every submitted field.

array_is_list() — Is It a Proper List? (PHP 8.1+)

<?php
var_dump(array_is_list(['a', 'b']));
var_dump(array_is_list([1 => 'a', 2 => 'b']));
var_dump(array_is_list(['x' => 'a']));
var_dump(array_is_list([]));

Output

bool(true)
bool(false)
bool(false)
bool(true)

Useful before json_encode() (a list becomes a JSON array; anything else becomes a JSON object) and for validating input that must be a simple list.

extract() — Use With Caution

extract($array) creates variables from array keys. On untrusted data (such as $_POST), it lets attackers overwrite any variable in scope, which is a serious security risk. Read the keys you need explicitly instead (see Variable Variables).

Practical Example: Paginating a List

<?php
function paginate(array $items, int $perPage, int $page): array
{
    $pages = array_chunk($items, $perPage);
    $totalPages = max(1, count($pages));
    $page = max(1, min($page, $totalPages));
    return [
        'items' => $pages[$page - 1] ?? [],
        'page' => $page,
        'totalPages' => $totalPages,
    ];
}
$products = array_map(fn(int $n): string => "Product $n", range(1, 7));
$result = paginate($products, 3, 2);
echo "Page {$result['page']} of {$result['totalPages']}: " . implode(', ', $result['items']) . "\n";
$last = paginate($products, 3, 99);
echo "Page {$last['page']} of {$last['totalPages']}: " . implode(', ', $last['items']) . "\n";

Output

Page 2 of 3: Product 4, Product 5, Product 6
Page 3 of 3: Product 7

Step-by-Step Explanation

1. range() and array_map() generate seven product names.
2. array_chunk() splits them into pages of three: [1–3], [4–6], [7].
3. The requested page is clamped into the valid range with max() and min(), so page 99 becomes the last page.
4. $pages[$page - 1] ?? [] selects the page (pages are numbered from 1, array indexes from 0) and returns an empty list if there are no items. For data stored in a database, paginate with LIMIT and OFFSET in the query instead of loading everything into an array (see Pagination with PHP and MySQL).

Common Mistakes

Assuming a Function Modifies the Array

Effect: array_reverse($list); alone does nothing visible. Fix: Assign the result: $list = array_reverse($list);.

Assuming a Function Returns the Array

Effect: $sorted = sort($list); stores true. Fix: Call in-place functions as statements, then use the original variable.

Ignoring Key Preservation

Effect: Gaps after array_filter(), array_diff(), or array_unique(); lost keys after array_merge() or sort(). Fix: Check how each function treats keys; use array_values() or key-preserving variants as needed.

Re-implementing Built-in Functions

Effect: More code and more bugs. Fix: Search this reference (or the manual) before writing a loop for a common task.

Best Practices

• Learn the categories; look up exact signatures in the manual when needed.
• Prefer functions that return new arrays for clearer, side-effect-free code.
• Pay attention to key preservation and strict comparison options.
• Use PHP 8.4+ functions (array_find(), array_any(), array_all()) and PHP 8.5+ functions (array_first(), array_last()) when your project's PHP version allows.
• Process large datasets in the database, and use array functions on the results. Official reference: https://www.php.net/manual/en/ref.array.php