Sorting multidimensional arrays using PHP

In PHP programming, we often need to sort multi-dimensional arrays to meet different needs, such as sorting by price, sorting in alphabetical order, etc. However, sorting multidimensional arrays is more complex than one-dimensional arrays. This article will introduce how to use PHP to sort multi-dimensional arrays.

1. PHP’s sorting function

First of all, we need to understand the sorting functions in PHP: sort(), rsort(), asort(), arsort(), ksort (), krsort(), uksort(), usort(). These functions are suitable for sorting one-dimensional arrays. If you want to sort a multi-dimensional array, we need to use a callback function to sort the array.

2. Definition of callback function

A callback function refers to a function passed as a parameter in other functions. In PHP, callback functions are usually used to sort, filter, traverse, etc. arrays. We can use an anonymous function or a function with a custom name as the callback function.

The following is an example of using an anonymous function as a callback function:

$array = array(
    array('price' => 45.50),
    array('price' => 15.00),
    array('price' => 20.15),
    array('price' => 25.00),
    array('price' => 90.10),
    array('price' => 9.99),
);

usort($array, function($a, $b) {
    if ($a['price'] == $b['price']) return 0;
    return ($a['price'] < $b['price']) ? -1 : 1;
});

print_r($array);

The output result is as follows:

Array (
    [0] => Array ( [price] => 9.99 )
    [1] => Array ( [price] => 15 )
    [2] => Array ( [price] => 20.15 )
    [3] => Array ( [price] => 25 )
    [4] => Array ( [price] => 45.5 )
    [5] => Array ( [price] => 90.1 )
)

3. Using the callback function to sort multi-dimensional arrays

If you want to sort a multi-dimensional array, we need to use a callback function to define the sorting rules of the array. We can define multiple sorting conditions in the callback function and compare the values ​​of the array elements one by one according to priority to achieve the purpose of sorting.

The following is an example of using a callback function to sort a multi-dimensional array:

$array = array(
    array('name' => 'John', 'age' => 25, 'score' => 80),
    array('name' => 'Mary', 'age' => 28, 'score' => 90),
    array('name' => 'Bob', 'age' => 20, 'score' => 95),
    array('name' => 'Jack', 'age' => 30, 'score' => 85),
    array('name' => 'Lisa', 'age' => 22, 'score' => 85),
);

// 按照年龄降序、分数升序、名字升序排序
usort($array, function($a, $b) {
    if ($a['age'] == $b['age']) {
        if ($a['score'] == $b['score']) {
            return strcmp($a['name'], $b['name']);
        } else {
            return ($a['score'] > $b['score']) ? 1 : -1;
        }
    } else {
        return ($a['age'] < $b['age']) ? 1 : -1;
    }
});

print_r($array);

The output results are as follows:

Array (
    [0] => Array ( [name] => Mary [age] => 28 [score] => 90 )
    [1] => Array ( [name] => Jack [age] => 30 [score] => 85 )
    [2] => Array ( [name] => Lisa [age] => 22 [score] => 85 )
    [3] => Array ( [name] => John [age] => 25 [score] => 80 )
    [4] => Array ( [name] => Bob [age] => 20 [score] => 95 )
)

4. Summary

This article introduces how to use PHP to implement sorting of multi-dimensional arrays. First we understand the sorting function in PHP, and then sort the multi-dimensional array through the callback function. In actual development, sorting is a very common function, and sorting multi-dimensional arrays can enable us to better meet various needs.

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