array_splice() / array_slice() Since: PHP 4（2000）

// Removes, inserts, or replaces elements at the specified position in an array.
array_splice(array, offset, length, replacement);

// Extracts a portion of an array and returns it as a new array.
array_slice(array, offset, length, preserve_keys);

<?php
$colors = ['red', 'blue', 'green', 'yellow', 'purple'];

// Extracts 2 elements starting at index 1. The original array is unchanged.
$sliced = array_slice($colors, 1, 2);
print_r($sliced); // Returns an array of ['blue', 'green'].

// Uses a negative offset to extract from the end.
$last_two = array_slice($colors, -2);
print_r($last_two); // Returns an array of ['yellow', 'purple'].

// Extracts elements while preserving the original keys.
$preserved = array_slice($colors, 2, 2, true);
print_r($preserved); // Keys are preserved as [2 => 'green', 3 => 'yellow'].

// Removes 2 elements starting at index 1 and inserts new elements.
$items = ['A', 'B', 'C', 'D', 'E'];
$removed = array_splice($items, 1, 2, ['X', 'Y', 'Z']);
print_r($removed); // Returns the removed elements ['B', 'C'].
print_r($items); // The array becomes ['A', 'X', 'Y', 'Z', 'D', 'E'].

// Inserts elements without removing any.
$list = ['Mon', 'Wed', 'Fri'];
array_splice($list, 1, 0, ['Tue']);
print_r($list); // The array becomes ['Mon', 'Tue', 'Wed', 'Fri'].

array_splice() is a destructive function that modifies the original array directly. It can delete, insert, and replace elements in a single call. Passing 0 as the third argument inserts without removing; omitting the fourth argument removes without inserting.

array_slice() is a non-destructive function that does not modify the original array. Passing true as the fourth argument preserves the original keys. By default, numeric keys are reindexed starting from 0, so specify true when key values are important.

If you only need to add or remove elements at the beginning or end of an array, array_push() / array_pop() / array_shift() / array_unshift() offer a simpler approach.