在php中usort()函数如何工作 [英] In php how does usort() function works

问题描述

我看过php文档，在线教程，但都没有找到usort如何实际工作.我下面有一个例子.

I have looked at the php documentation, tutorials online and none of them how usort is actually working. I have an example i was playing with below.

$data = array(

    array('msg' => 'some text','month' => 11,'level' => 10),

    array('msg' => 'some text','month' => 5,'level' => 10),

    array('msg' => 'some text','month' => 8,'level' => 10),

    array('msg' => 'some text','month' => 12,'level' => 10),

    array('msg' => 'some text','month' => 2,'level' => 10),

    array('msg' => 'some text','month' => 3,'level' => 10),

    array('msg' => 'some text','month' => 4,'level' => 10),

    array('msg' => 'some text','month' => 7,'level' => 10),

    array('msg' => 'some text','month' => 10,'level' => 10),

    array('msg' => 'some text','month' => 1,'level' => 10),

    array('msg' => 'some text','month' => 6,'level' => 10),

    array('msg' => 'some text','month' => 9,'level' => 10)

);

我希望能够将月份从12排序为1(因为它们是无组织的) 通过一些帮助，这就是解决方案

I wanted to be able to sort the months from 12 to 1 (since their unorganized) through some help this was the solution

function cmp($a, $b)
{
    if ($a["month"] == $b["month"]) 
    {
       return 0;
    }
    return ($a["month"] < $b["month"]) ? -1 : 1;
}

usort($data, "cmp");

但是我不明白函数cmp如何对数组进行排序.我试图像这样打印出每个变量$ a和$ b:

but i dont understand how the function cmp sorts the array. i tried printing out each variable $a and $b like this:

function cmp($a, $b)
{
   echo "a: ".$a['month']."<br/>";
   echo " b: ".$b['month']."<br/>";
   echo "<br/><br/>";
}

输出为

a: 3
b: 5

a: 9
b: 3

a: 3
b: 8

a: 6
b: 3

a: 3
b: 12

a: 1
b: 3

a: 3
b: 2

a: 10
b: 3

a: 3
b: 11

a: 7
b: 3

a: 4
b: 3

a: 12
b: 2

a: 5
b: 12

a: 12
b: 11

a: 8
b: 12

a: 5
b: 8

a: 2
b: 11

a: 6
b: 9

a: 7
b: 6

a: 6
b: 4

a: 10
b: 6

a: 1
b: 6

a: 9
b: 4

a: 7
b: 1

a: 10
b: 7

对于排序如何工作以及为什么使用cmp($ a，$ b)没有意义.如您所见，我已经尝试打印出其所有流程，但尚未对所有流程进行任何解决..

it makes no sense to how the sort is working and why cmp($a, $b) is used. i have tried to print out all its processes as you can see but have not come to any solution to how it all works..

谢谢

推荐答案

函数cmp本身不进行排序.它只是告诉usort一个值是否小于，等于或大于另一个值.例如.如果$a = 5和$b = 9，它将返回1表示$b中的值大于$a中的值.

The function cmp itself doesn't do the sorting. It just tells usort if a value is smaller, equal or greater than another value. E.g. if $a = 5 and $b = 9 it will return 1 to indicate that the value in $b is greater than the one in $a.

排序由usort完成.

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