How to sort elements in an array in php

In PHP, for sorting of 2-dimensional arrays, you can use the built-in functions usort() and uasort() to achieve it. Both functions can sort elements in an array, but the implementation is slightly different. The

usort() function will sort the original array and return a Boolean value, while the uasort() function will sort the original array but retain the key-value pairs The association between them means that no new index array is created. Below we will introduce how to use these two functions respectively.

usort()Function

usort()The first parameter of the function is the array that needs to be sorted, and the second parameter is a comparison Function, which is implemented by exchanging the positions of elements in the array that needs to be sorted and returning a Boolean value.

//示例数组$students
$students = array(
    array("name" => "张三", "age" => 22),
    array("name" => "李四", "age" => 20),
    array("name" => "王五", "age" => 25)
);

//比较函数cmp
function cmp($a, $b){
    if ($a["age"] == $b["age"]) {
        return 0;
    }
    return ($a["age"] < $b["age"]) ? -1 : 1;
}

//使用usort()排序
usort($students, "cmp");

//输出结果
var_dump($students);

In the above code, we first define a 2-dimensional array $students containing three elements, each element contains two key-value pairs "name" and "age".

Next, we define a comparison function cmp, which determines the relative order between elements by comparing the values ​​of two elements on the "age" key-value pair. If the "age" of the two elements is equal, 0 is returned; if the "age" of $a is less than the "age" of $b, then -1 is returned, indicating that $a is in front of $b; otherwise, 1 is returned, indicating that $a After $b.

Finally, we use the usort() function to sort the array $students according to the rules defined by the cmp function. From the output, you can see that the elements in the array have been sorted from small to large according to the "age" key-value pair.

uasort()Function

uasort()The implementation of the function is similar to usort(), but different It retains the association between key-value pairs and does not create a new index array. Therefore, it requires a more complex comparison function that not only compares element sizes but also maintains the association of key-value pairs.

//示例数组$students
$students = array(
    "stu1" => array("name" => "张三", "age" => 22),
    "stu2" => array("name" => "李四", "age" => 20),
    "stu3" => array("name" => "王五", "age" => 25)
);

//比较函数cmp
function cmp($a, $b){
    if ($a["age"] == $b["age"]) {
        return 0;
    }
    return ($a["age"] < $b["age"]) ? -1 : 1;
}

//使用usort()排序
uasort($students, "cmp");

//输出结果
var_dump($students);

In the above code, we first define a 2-dimensional associative array $students containing three elements, each element contains two key-value pairs "name" and "age". The difference is that here we use the strings "stu1", "stu2" and "stu3" as the key values ​​of the array instead of the previous numeric index.

The way to define the comparison function cmp is the same as usort(). The difference is that when we call the uasort() function, we pass the array $students and the comparison function cmp as parameters. This function will sort the array according to the cmp rules, and the sorted result retains the original joint key-value relationship.

Finally, we output the sorting results through the var_dump() function. As you can see, the output result is still an associative array, but the elements have been sorted from small to large according to the "age" key-value pair.

In addition to usort() and uasort(), PHP also provides a series of other array sorting functions, such as asort() , arsort(), ksort(), krsort(), etc. Developers can choose the appropriate function according to actual needs.

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