How to sort multidimensional array in PHP

How to sort multidimensional arrays in PHP

In PHP, arrays are a very common and important data structure, and multidimensional arrays are used more frequently in some complex data processing. . However, sorting multidimensional arrays can be tricky. This article will show you how to sort multidimensional arrays in PHP and provide specific code examples.

Before we begin, let’s first understand the structure of multi-dimensional arrays. Multidimensional array means that the elements in an array are also an array, forming a nested structure. For example:

$students = array(
    array('name' => 'John', 'age' => 19),
    array('name' => 'Emily', 'age' => 21),
    array('name' => 'Tom', 'age' => 18)
);

In the above example, $students is an array containing 3 elements, each element is an associative array, containing the name and age of the student. We will use this array as an example to sort.

For sorting multi-dimensional arrays, the most common method is to use the usort() function. The usort() function allows us to sort an array according to a specified sorting rule. Here is a simple example that demonstrates how to sort students by age:

usort($students, function($a, $b){
    return $a['age'] - $b['age'];
});

// 打印排序后的结果
print_r($students);

With the above code, we are using an anonymous function as the second parameter of the usort() function. This anonymous function accepts two parameters $a and $b, which represent two elements in the array respectively. In our example, they are the information of two students. We determine the order of two students by comparing their ages.

In the anonymous function, return $a['age'] - $b['age'] determines the sorting method. If the return value is a negative number, then $a should be sorted before $b; if the return value is a positive number, then $a should be sorted after $b; if the return value is 0, then the order of $a and $b will not change. .

After running the above code, you will get the following results:

Array
(
    [0] => Array
        (
            [name] => Tom
            [age] => 18
        )

    [1] => Array
        (
            [name] => John
            [age] => 19
        )

    [2] => Array
        (
            [name] => Emily
            [age] => 21
        )
)

You can see that the students in the array are arranged in order from small to large in age.

In addition to sorting by age in the example, we can also sort multidimensional arrays based on other fields. For example, we can sort based on students' names:

usort($students, function($a, $b){
    return strcmp($a['name'], $b['name']);
});

// 打印排序后的结果
print_r($students);

In this example, we have used the strcmp() function to compare students' names. The strcmp() function compares two strings in alphabetical order and returns the corresponding integer based on the comparison result. In our example, return strcmp($a['name'], $b['name']) determines the order of student names.

After running the above code, you will get the following results:

Array
(
    [0] => Array
        (
            [name] => Emily
            [age] => 21
        )

    [1] => Array
        (
            [name] => John
            [age] => 19
        )

    [2] => Array
        (
            [name] => Tom
            [age] => 18
        )
)

You can see that the students in the array are arranged in order from A to Z by name.

Summary:

Sorting multi-dimensional arrays in PHP is not complicated. By using the usort() function and appropriate sorting rules, we can easily sort multi-dimensional arrays. You can better understand how to apply these sorting methods with the code examples shown in this article. I hope this article can help you when dealing with multi-dimensional arrays.

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