Array Functions

PHP provides many built-in functions for array manipulation. This page serves as a quick reference organized by use case.

For basic array operations (creating, accessing, adding, removing elements), see PHP Arrays.

PHP Array Functions - Full Documentation ↗

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Array Information

count()

Returns the number of elements.

$fruits = ['apple', 'banana', 'orange'];
echo count($fruits);  // 3

is_array()

Checks if a variable is an array.

is_array(['a', 'b']);  // true
is_array('hello');     // false

array_key_exists()

Checks if a key exists (works even when the value is null).

$user = ['name' => 'John', 'email' => null];

array_key_exists('email', $user);  // true
isset($user['email']);             // false (null treated as not set)

in_array()

Checks if a value exists.

$fruits = ['apple', 'banana', 'orange'];

in_array('banana', $fruits);        // true
in_array('4', [1, 2, 3, 4]);        // true (loose comparison)
in_array('4', [1, 2, 3, 4], true);  // false (strict comparison)

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Keys and Values

array_keys()

Returns all keys.

$person = ['name' => 'John', 'age' => 30];
array_keys($person);  // ['name', 'age']

array_values()

Returns all values with numeric keys.

$person = ['name' => 'John', 'age' => 30];
array_values($person);  // ['John', 30]

array_flip()

Swaps keys and values.

$original = ['a' => 1, 'b' => 2];
array_flip($original);  // [1 => 'a', 2 => 'b']

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Searching and Filtering

array_search()

Finds the key for a given value.

$fruits = ['apple', 'banana', 'orange'];
array_search('banana', $fruits);  // 1
array_search('grape', $fruits);   // false

array_filter()

Filters elements using a callback.

$numbers = [1, 2, 3, 4, 5, 6];

$evens = array_filter($numbers, fn($n) => $n % 2 === 0);
// [2, 4, 6]

array_column()

Extracts a column from a multidimensional array.

$users = [
    ['id' => 1, 'name' => 'John'],
    ['id' => 2, 'name' => 'Jane']
];

array_column($users, 'name');         // ['John', 'Jane']
array_column($users, 'name', 'id');   // [1 => 'John', 2 => 'Jane']

array_unique()

Removes duplicate values.

$colors = ['red', 'blue', 'red', 'green'];
array_unique($colors);  // ['red', 'blue', 'green']

array_intersect()

Returns values present in all arrays.

$a = ['a', 'b', 'c'];
$b = ['b', 'c', 'd'];
array_intersect($a, $b);  // ['b', 'c']

array_diff()

Returns values from the first array not present in others.

$a = ['a', 'b', 'c', 'd'];
$b = ['b', 'c'];
array_diff($a, $b);  // ['a', 'd']

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Transforming Arrays

array_map()

Applies a callback to each element.

$numbers = [1, 2, 3, 4];
$squared = array_map(fn($n) => $n * $n, $numbers);
// [1, 4, 9, 16]

array_walk()

Applies a callback that can modify elements in place.

$prices = ['apple' => 1.50, 'banana' => 0.75];

array_walk($prices, function(&$price) {
    $price = round($price * 1.08, 2);  // Add 8% tax
});
// ['apple' => 1.62, 'banana' => 0.81]

array_reduce()

Reduces an array to a single value.

$numbers = [1, 2, 3, 4, 5];
$sum = array_reduce($numbers, fn($carry, $n) => $carry + $n, 0);
// 15

array_chunk()

Splits an array into chunks.

$data = [1, 2, 3, 4, 5, 6];
array_chunk($data, 2);  // [[1, 2], [3, 4], [5, 6]]

array_slice()

Extracts a portion of an array.

$fruits = ['apple', 'banana', 'orange', 'grape'];
array_slice($fruits, 1, 2);  // ['banana', 'orange']
array_slice($fruits, -2);    // ['orange', 'grape']

array_reverse()

Reverses element order.

$numbers = [1, 2, 3];
array_reverse($numbers);  // [3, 2, 1]

implode() and explode()

Convert between arrays and strings.

$fruits = ['apple', 'banana', 'orange'];
implode(', ', $fruits);  // "apple, banana, orange"

$text = "one,two,three";
explode(',', $text);  // ['one', 'two', 'three']

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Combining Arrays

array_merge()

Merges arrays together.

$a = ['a', 'b'];
$b = ['c', 'd'];
array_merge($a, $b);  // ['a', 'b', 'c', 'd']

// With associative arrays, later values overwrite earlier ones
$defaults = ['color' => 'blue', 'size' => 'M'];
$custom = ['color' => 'red'];
array_merge($defaults, $custom);  // ['color' => 'red', 'size' => 'M']

array_combine()

Creates an array using one array for keys and another for values.

$keys = ['name', 'email'];
$values = ['John', 'john@example.com'];
array_combine($keys, $values);  // ['name' => 'John', 'email' => 'john@example.com']

array_replace()

Replaces values by key.

$base = ['a' => 1, 'b' => 2];
$new = ['b' => 20, 'c' => 3];
array_replace($base, $new);  // ['a' => 1, 'b' => 20, 'c' => 3]

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Sorting

All sorting functions modify the array in place.

By Value

Function	Order	Maintains Keys
sort()	Ascending	No
rsort()	Descending	No
asort()	Ascending	Yes
arsort()	Descending	Yes

$fruits = ['orange', 'apple', 'banana'];
sort($fruits);  // ['apple', 'banana', 'orange']

$ages = ['John' => 25, 'Jane' => 30, 'Bob' => 20];
asort($ages);  // ['Bob' => 20, 'John' => 25, 'Jane' => 30]

By Key

Function	Order
ksort()	Ascending
krsort()	Descending

$data = ['c' => 3, 'a' => 1, 'b' => 2];
ksort($data);  // ['a' => 1, 'b' => 2, 'c' => 3]

Custom Sorting

Use usort() for custom comparison logic. The spaceship operator (<=>) returns -1, 0, or 1.

$people = [
    ['name' => 'John', 'age' => 25],
    ['name' => 'Jane', 'age' => 30],
    ['name' => 'Bob', 'age' => 20]
];

usort($people, fn($a, $b) => $a['age'] <=> $b['age']);
// Sorted by age: Bob (20), John (25), Jane (30)

Use uasort() to preserve keys, or uksort() to sort by keys with custom logic.

Sorting Flags

$data = ['10', '2', '1', '20'];

sort($data);                // ['1', '10', '2', '20'] (string comparison)
sort($data, SORT_NUMERIC);  // ['1', '2', '10', '20'] (numeric comparison)