php two-dimensional array flip

1. Preface

In PHP, array (Array) is one of the common data structures. An array is composed of several elements (Element), and each element has a unique index (Index). Arrays in PHP can be one-dimensional, two-dimensional, or even multi-dimensional. In development, we often need to operate on arrays, and one of the common operations is array flipping. Below we will introduce in detail how to flip a two-dimensional array in PHP.

2. What is array flipping?

In a two-dimensional array, we usually perform operations such as sorting and filtering according to a certain dimension. However, if we need to perform a reverse operation on the array, that is, flip the two-dimensional array along a certain dimension to achieve the purpose of changing the array structure, this operation is called array flipping.

For example, suppose we have a two-dimensional array $originalArr, which stores a series of information about the PHP framework:

$originalArr = array(
    array("name" => "Laravel", "year" => "2011", "author" => "Taylor Otwell"),
    array("name" => "Symfony", "year" => "2005", "author" => "Fabien Potencier"),
    array("name" => "CodeIgniter", "year" => "2006", "author" => "EllisLab"),
    array("name" => "CakePHP", "year" => "2005", "author" => "Cake Software Foundation")
);

If we want to use the year as the first dimension of the array After flipping, you can get the following new array $flippedArr:

$flippedArr = array(
    "2011" => array("name" => "Laravel", "year" => "2011", "author" => "Taylor Otwell"),
    "2005" => array("name" => "Symfony", "year" => "2005", "author" => "Fabien Potencier"),
    "2006" => array("name" => "CodeIgniter", "year" => "2006", "author" => "EllisLab"),
    "2005" => array("name" => "CakePHP", "year" => "2005", "author" => "Cake Software Foundation")
);

You can see that the one-dimensional array indexed by year in the new array replaces the first dimension in the original array, thus achieving the flipped Purpose.

3. How to implement two-dimensional array flipping

In PHP, two-dimensional array flipping can be achieved through the following two methods.

• Use the array sorting function

PHP provides powerful array sorting functions such as sort() and rsort(), which can perform ascending and descending order on two-dimensional arrays. Wait for sorting operations. Among them, the sort() function can sort the array in ascending order according to the first dimension, while the rsort() function can sort the array in descending order. If we sort the array according to the value of a certain index, we can achieve the effect of flipping. For example, if we use the following code:

array_multisort(array_column($originalArr, "year"), SORT_DESC, $originalArr);

, we can get a new array $flippedArr sorted in reverse order by year.

• Use row-by-row traversal method

The row-by-row traversal method refers to accessing each element in the two-dimensional array one by one, and then actively adding elements to it according to certain rules. in the new array. For example, we can use the following code:

$flippedArr = array();
foreach ($originalArr as $value) {
    $flippedArr[$value['year']] = $value;
}

In this way, we can get the same flipped new array.

4. Summary

For PHP developers, mastering array operations is extremely important. Among them, array flipping is a common operation that can help us change the structure of the array and increase the readability and maintainability of the code. Through the introduction of this article, we understand the implementation method of two-dimensional array flipping, and use specific example codes to help readers better master it. It is hoped that readers can effectively use this knowledge in daily development and contribute to the success of the project.

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