array_unshift()
array_unshift() prepends one or more elements to the beginning of an array. All numeric keys are reset starting from zero, while string keys remain unchanged. The function returns the new number of elements in the array.
array_unshift() is the opposite of array_shift(), which removes and returns the first element. Together with array_push() and array_pop(), these four functions are used to implement queue, FIFO, or stack, LIFO, data structures.
Note that array_unshift() is an O(n) operation because all integer keys must be renumbered.
<?php
$array = [1, 2, 3];
$count = array_unshift($array, 0);
// $array == [0, 1, 2, 3], $count == 4
// Prepend multiple elements
array_unshift($array, -2, -1);
// $array == [-2, -1, 0, 1, 2, 3]
// String keys are preserved; integer keys are reset
$assoc = ['b' => 2, 'c' => 3];
array_unshift($assoc, 1);
// $assoc == [0 => 1, 'b' => 2, 'c' => 3]
?>