How to set the array header to increase in php

In PHP, there are many ways to add elements to the head of an array. In this article, we will introduce two common methods, one is to use the array_unshift function, and the other is to use the " " operator. The following is a detailed explanation:

Method 1: Use the array_unshift function

The array_unshift function can add one or more elements to the head of the array. The syntax of this function is as follows:

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

where $array is the target array to which elements are to be added. , $value1 is the element to be added. If you want to add multiple elements, you can add multiple parameters later, each parameter represents an element to be added. The return value of this function is the new length of the array after adding elements.

The following is an example that demonstrates how to use the array_unshift function to add an element to the head of an array:

// 原始数组
$fruits = array("apple", "banana", "orange");

// 在数组头部增加一个元素
array_unshift($fruits, "pear");

// 输出新数组
print_r($fruits);

The above code output:

Array
(
    [0] => pear
    [1] => apple
    [2] => banana
    [3] => orange
)

Method 2: Use the " " operator

The " " operator can perform merge operations between two arrays. If there are identical elements in the arrays, the elements in the first array are retained and the elements in the second array are not overwritten or added.

By converting the original array into a key index array, we can use the " " operator to add an element to the head of the array. The following is the sample code:

// 原始数组
$fruits = array("apple", "banana", "orange");

// 转换为键名索引数组
$fruits = array_reverse($fruits, true);

// 在数组头部增加一个元素
$fruits = array("pear") + $fruits;

// 转换为数字索引数组
$fruits = array_reverse($fruits);

// 输出新数组
print_r($fruits);

The above code output:

Array
(
    [0] => pear
    [1] => apple
    [2] => banana
    [3] => orange
)

As you can see, we first convert the original array into a key index array by using the array_reverse function, and then use the " " operator to Add an element to the head of the array, and finally convert the array back to numerical indexing.

Note:

No matter which method is used, adding elements to the head of the array will change the subscript of the array. Therefore, if you need to preserve the original subscript, use the array_unshift function to add elements to the beginning of the array. If you do not need to preserve the original subscript, you can use the " " operator to add elements to the head of the array.

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