在 php 中 usort() 函数是如何工作的
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In php how does usort() function works
提问by Sarmen B.
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.
我已经查看了 php 文档、在线教程，但没有一个了解 usort 的实际工作方式。我有一个我在下面玩的例子。
$data = array(
array('msg' => 'some text','month' => 11,'level' => 10),
array('msg' => 'some text','month' => 5,'level' => 10),
array('msg' => 'some text','month' => 8,'level' => 10),
array('msg' => 'some text','month' => 12,'level' => 10),
array('msg' => 'some text','month' => 2,'level' => 10),
array('msg' => 'some text','month' => 3,'level' => 10),
array('msg' => 'some text','month' => 4,'level' => 10),
array('msg' => 'some text','month' => 7,'level' => 10),
array('msg' => 'some text','month' => 10,'level' => 10),
array('msg' => 'some text','month' => 1,'level' => 10),
array('msg' => 'some text','month' => 6,'level' => 10),
array('msg' => 'some text','month' => 9,'level' => 10)
);
I wanted to be able to sort the months from 12 to 1 (since their unorganized) through some help this was the solution
我希望能够通过一些帮助将月份从 12 排序到 1（因为它们是无组织的）这是解决方案
function cmp($a, $b)
{
if ($a["month"] == $b["month"])
{
return 0;
}
return ($a["month"] < $b["month"]) ? -1 : 1;
}
usort($data, "cmp");
but i dont understand how the function cmp sorts the array. i tried printing out each variable $a and $b like this:
但我不明白函数 cmp 如何对数组进行排序。我试着像这样打印出每个变量 $a 和 $b：
function cmp($a, $b)
{
echo "a: ".$a['month']."<br/>";
echo " b: ".$b['month']."<br/>";
echo "<br/><br/>";
}
and the output was
输出是
a: 3
b: 5
a: 9
b: 3
a: 3
b: 8
a: 6
b: 3
a: 3
b: 12
a: 1
b: 3
a: 3
b: 2
a: 10
b: 3
a: 3
b: 11
a: 7
b: 3
a: 4
b: 3
a: 12
b: 2
a: 5
b: 12
a: 12
b: 11
a: 8
b: 12
a: 5
b: 8
a: 2
b: 11
a: 6
b: 9
a: 7
b: 6
a: 6
b: 4
a: 10
b: 6
a: 1
b: 6
a: 9
b: 4
a: 7
b: 1
a: 10
b: 7
it makes no sense to how the sort is working and why cmp($a, $b) is used. i have tried to print out all its processes as you can see but have not come to any solution to how it all works..
排序如何工作以及为什么使用 cmp($a, $b) 是没有意义的。正如你所看到的，我试图打印出它的所有进程，但还没有找到任何关于它如何工作的解决方案。
thanks
谢谢
回答by halfdan
The function cmpitself doesn't do the sorting. It just tells usortif a value is smaller, equal or greater than another value. E.g. if $a = 5and $b = 9it will return 1 to indicate that the value in $bis greater than the one in $a.
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 if $a = 5and$b = 9它将返回 1 表示 in 的值$b大于in 的值$a。
Sorting is done by usort.
排序由usort.
回答by knittl
The callback provided to the sorting functions in PHP have three return values:
PHP 中提供给排序函数的回调有三个返回值：
0: both elements are the same
-1 (<0): the first element is smaller than the second
1 (>0): the first element is greater
Now, usortprobably uses some kind of quicksort or mergesort internally. For each comparison it calls your callback with two elements and then decides if it needs to swap them or not.
现在，usort可能在内部使用某种快速排序或归并排序。对于每次比较，它会使用两个元素调用您的回调，然后决定是否需要交换它们。
回答by Paul
回答by pat
As the others mentioned, usort uses the Quicksort algorithm. On a side note, you do not need to explicitly do the comparision between two strings. You can use PHP's string compare methods.
正如其他人提到的，usort 使用 Quicksort 算法。附带说明一下，您不需要明确地在两个字符串之间进行比较。您可以使用 PHP 的字符串比较方法。
The function that you created,
您创建的函数，
function cmp($a, $b)
{
if ($a["month"] == $b["month"])
{
return 0;
}
return ($a["month"] < $b["month"]) ? -1 : 1;
}
could simply be written as follows
可以简单地写成如下
function compareMyStrings($a, $b){
return strnatcmp($a["month"], $b["month"]);
}
Hope this helps!
希望这可以帮助！
回答by Lead Developer
This is another solution I found
这是我发现的另一个解决方案
<?php
$users = array( array( "peter", "male", "46"),
array( "hans", "male", "19"),
array( "john", "male", "30"),
array( "linda", "female", "54"),
array( "erika", "female", "79"));
usort($users, "whatevername");
function whatevername($whatever1, $whatever2)
{
// $whatever1 and $whatever2 are items from the $user array.
// index [2] is the age.
// Check if $whatever1 is older than $whatever2.
// Return 1 tells usort to swap the positions.
return $whatever1[2] > $whatever2[2];
}
echo("<pre>");
print_r($users);
echo("</pre>");
?>
