How to change array index in php

In PHP, we often need to change the index of an array, such as rearranging the index, or changing the index value of a specific element. This article will introduce some commonly used PHP functions and techniques to help you easily modify array indexes.

1. Use the array_values() function to rearrange the indexes

If your array contains discontinuous indexes and you want to rearrange these indices, you can use the array_values() function. This function can return a new array in which the elements remain unchanged but their indexes are rearranged in order.

For example, suppose you have the following array:

$fruits = array(2 => 'apple', 4 => 'banana', 6 => 'orange');

The indexes of this array are not consecutive. If you print the array using the print_r() function, you will see the following output:

Array
(
    [2] => apple
    [4] => banana
    [6] => orange
)

To rearrange the indexes, pass the array to the array_values() function as follows:

$fruits = array_values($fruits);

Now, the indexes of the array have been rearranged as follows:

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

Please note that this function returns a new array without modifying the original array. Therefore, you need to assign the returned array to the original array in order to achieve the change of index.

2. Use the unset() function to delete the elements and reassign them with new keys

Another way is to use the unset() function to delete the elements in the original array and use the new ones Key reassignment. For example, let's say you have the following array:

$colors = array('red', 'green', 'blue');

Now, let's say you want to remove the 'green' element and use 'purple' as its new key. You can use the unset() function to remove the element and reassign it with the new array element:

unset($colors[1]); // 删除'green'元素
$colors['purple'] = 'blue'; // 使用'purple'作为键重新分配'blue'元素

Now, the array looks like this:

Array
(
    [0] => red
    [purple] => blue
)

Please note that using this method, You need to be careful to avoid conflicts with new keys. If the new key conflicts with an existing key, it will overwrite that key's value.

3. Use the array_combine() function to combine two arrays into a new array

Sometimes, you may need to combine two arrays into a new array and use the keys of one of the arrays as the key of the new array. For example, suppose you have the following two arrays:

$keys = array('name', 'email', 'phone');
$values = array('John', 'john@example.com', '123-456-7890');

Now, suppose you want to use the elements in the $keys array as keys for the new array, and the elements in the $values ​​array as values ​​in the new array. You can combine these two arrays into a new array using the array_combine() function:

$contact = array_combine($keys, $values);

Now, the $contact array looks like this:

Array
(
    [name] => John
    [email] => john@example.com
    [phone] => 123-456-7890
)

Please note that both arrays must have The same number of elements. If the two arrays have different numbers of elements, a warning will be triggered and FALSE will be returned.

4. Use the array_map() function to map a new key to each element

If you want to assign a new key to each element without modifying the original array, you You can use the array_map() function. This function applies a function to each element of the specified array and returns a new array.

For example, let's say you have the following array:

$names = array('John', 'Jane', 'Bob');

Now, let's say you want to map that array into a new array using the index numbers as keys. You can achieve this using the array_map() function and an anonymous function:

$names = array_map(function ($value, $index) {
    return array(
        'id' => $index,
        'name' => $value
    );
}, $names, array_keys($names));

Now, the $names array looks like this:

Array
(
    [0] => Array
        (
            [id] => 0
            [name] => John
        )

    [1] => Array
        (
            [id] => 1
            [name] => Jane
        )

    [2] => Array
        (
            [id] => 2
            [name] => Bob
        )
)

Please note that the function will return a new array. The original array will be unaffected.

Summary

In PHP, you can use several methods to change the index of an array. Whether you are rearranging the index or assigning a new key to each element, there are a variety of techniques and functions to choose from. Please choose the appropriate method based on your specific needs, taking care to avoid possible key conflicts.

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