How to swap array keys and values ​​in php

In PHP, sometimes it is necessary to exchange the keys and values ​​in the array. For example, convert an array with numbers as keys to an associative array with values ​​as keys. Novices may think this is difficult to implement, but in fact, PHP provides a very simple way to achieve this function. In this article, we will learn how to transpose array keys and values ​​using PHP.

Method 1: Use the array_flip function

In PHP, you can use the array_flip function to exchange the keys and values ​​in the array. This function takes an array as input and returns a new array with the original values ​​as keys and the original keys as values. For example:

$numbers = array(1, 2, 3, 4, 5);
$flipped_numbers = array_flip($numbers);

print_r($flipped_numbers);

// Output:
// Array
// (
//     [1] => 0
//     [2] => 1
//     [3] => 2
//     [4] => 3
//     [5] => 4
// )

In the above example, we pass an array with numbers as keys to the array_flip function and save the returned result into the $flipped_numbers variable. This function takes the values ​​of the original array as the keys of the new array, and the keys of the original array as the values ​​of the new array. Therefore, the keys in the $flipped_numbers array are the numbers 1 to 5, and the values ​​are the keys of the original array.

Please note that if there are multiple identical values ​​in the original array, an error will be reported when calling the array_flip function, because the same value cannot be the key of the new array at the same time.

Method 2: Use foreach loop

In addition to using the array_flip function, we can also use foreach loop to exchange the keys and values ​​of the array. This approach requires iterating over the original array and using a new associative array to hold the results. In each loop, use the keys of the original array as the values ​​of the new array, and the values ​​of the original array as the keys of the new array. For example:

$numbers = array(1, 2, 3, 4, 5);
$flipped_numbers = array();

foreach ($numbers as $key => $value) {
    $flipped_numbers[$value] = $key;
}

print_r($flipped_numbers);

// Output:
// Array
// (
//     [1] => 0
//     [2] => 1
//     [3] => 2
//     [4] => 3
//     [5] => 4
// )

In the above example, we first define an empty associative array $flipped_numbers. We then use a foreach loop to iterate over the original array $numbers. In each loop, we save the key of the original array (i.e. the index) into the $value variable and the value of the original array (i.e. the number) into the $key variable. Then, we use $key as the key of the new array $flipped_numbers and $value as the value of the new array. So, the keys in the $flipped_numbers array are the numbers 1 to 5, and the values ​​are the keys of the original array.

Please note that when using a foreach loop, you must ensure that the values ​​in the original array are unique, otherwise the same key will appear. This situation will also occur when using the array_flip function.

Summary

In this article, we learned two ways to swap array keys and values ​​using PHP. The first way is to use the array_flip function which uses the values ​​of the original array as the keys of the new array and the keys of the original array as the values ​​of the new array. The second method is to use a foreach loop, iterate over the original array and swap the keys and values ​​of the original array and save it to a new associative array. Depending on the usage scenario, you can flexibly choose between these two methods. It should be noted that if there are duplicate values ​​in the original array, you cannot use these two methods to swap the keys and values ​​of the original array.

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