How to insert at the head of an array in php

In PHP, an array is a very common data type that can store multiple values ​​and access them through indexes. When we need to add elements to an array, we usually use the insertion method at the end of the array, that is, using array_push() or the syntax sugar of []. However, in some cases, we need to insert elements at the head of the array, in which case we need to use the array_unshift() function.

The array_unshift() function can accept one or more parameters. Each parameter will be inserted into the head of the array and new elements will be added in front of existing elements. The syntax of this function is as follows:

array_unshift(array &$array, mixed $value1 [, mixed $... ])

Among them, $array is the array into which elements need to be inserted, and the & symbol Indicates passing by reference, so that modifications can be made directly on the original array. $value1 is the first element that needs to be inserted, and the following $... indicates that multiple elements can be inserted.

The following is a simple example:

$arr = array('a', 'b', 'c');
array_unshift($arr, 'x', 'y', 'z');
print_r($arr);

Output:

Array
(
    [0] => x
    [1] => y
    [2] => z
    [3] => a
    [4] => b
    [5] => c
)

In the above example, we inserted three into the array $arr through the array_unshift() function elements, namely x, y and z. These three elements are inserted into the head of the original array, and the elements in the original array are moved backward three positions in sequence.

It should be noted that the array_unshift() function will return the number of elements in the array after the operation, rather than returning a new array. If you want to get a new array, you can use the array_merge() function to merge the element array to be inserted with the original array.

$arr = array('a', 'b', 'c');
$new_arr = array_merge(array('x', 'y', 'z'), $arr);
print_r($new_arr);

Output:

Array
(
    [0] => x
    [1] => y
    [2] => z
    [3] => a
    [4] => b
    [5] => c
)

To summarize, using the array_unshift() function can easily insert elements at the head of the array, which is very useful for some specific scenarios. If you need to make modifications to the original array, you can directly use the array_unshift() function. If you need to get a new array, you can use the array_merge() function.

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