usort()

(PHP 4, PHP 5, PHP 7)

使用用户自定义的比较函数对数组中的值进行排序

说明

本函数将用用户自定义的比较函数对一个数组中的值进行排序。如果要排序的数组需要用一种不寻常的标准进行排序，那么应该使用此函数。

If two members compare as equal, their relative order in the sorted array is undefined.Note:此函数为$array中的元素赋与新的键名。这将删除原有的键名，而不是仅仅将键名重新排序。

参数

输入的数组

在第一个参数小于，等于或大于第二个参数时，该比较函数必须相应地返回一个小于，等于或大于 0 的整数。

Returningnon-integervalues from the comparison function, such asfloat, will result in an internal cast tointegerof the callback's return value. So values such as 0.99 and 0.1 will both be cast to an integer value of 0, which will compare such values as equal.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

范例

Example #1usort()例子

以上例程会输出：

0: 1
1: 2
2: 3
3: 5
4: 6

Note:

很明显在这个小例子中用sort()函数更合适。

使用多维数组的usort()例子

当排序多维数组时，$a和$b包含到数组第一个索引的引用。

以上例程会输出：

$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons

Example #3usort()example using a member function of an object

以上例程会输出：

b
c
d

Example #4usort()example using aclosureto sort a multi-dimensional array

以上例程会输出：

y, a
x, b
z, c

参见

• uasort() 使用用户自定义的比较函数对数组中的值进行排序并保持索引关联
• 数组排序函数对比

Just wanted to show off the beauty of PHPs spaceship operator in this use case. 

When trying to do some custom sorting with objects and an anonymous function it wasn't entirely clear how this usort function works. I think it probably uses a quicksort in the background. Basically it actually moves the $b variable up or down in respect to the $a variable. It does NOT move the $a variable inside the callback function. This is key to getting your logic right in the comparisons.
If you return -1 that moves the $b variable down the array, return 1 moves $b up the array and return 0 keeps $b in the same place. 
To test I cut down my code to sorting a simple array from highest priority to lowest.

Output:
b (8) is higher priority than a (3), moving b up array
b (5) is higher priority than a (3), moving b up array
b (7) is higher priority than a (3), moving b up array
a (3) is same priority as b (3), keeping the same
a (8) is higher priority than b (3), moving b down array
b (8) is higher priority than a (7), moving b up array
b (8) is higher priority than a (5), moving b up array
b (8) is higher priority than a (3), moving b up array
a (5) is higher priority than b (3), moving b down array
a (7) is higher priority than b (5), moving b down array
Sorted priorities:
array(5) {
 [0]=> int(8)
 [1]=> int(7)
 [2]=> int(5)
 [3]=> int(3)
 [4]=> int(3)
}

You can also sort multi-dimensional array for multiple values like as

Output:
Array
(
  [0] => Array
    (
      [name] => Jackson
      [nick_name] => jack
      [availability] => 1
      [is_fav] => 1
    )
  [1] => Array
    (
      [name] => David
      [nick_name] => dav07
      [availability] => 0
      [is_fav] => 1
    )
  [2] => Array
    (
      [name] => Zen
      [nick_name] => zen
      [availability] => 1
      [is_fav] => 0
    )
  [3] => Array
    (
      [name] => Rohit
      [nick_name] => rod
      [availability] => 0
      [is_fav] => 0
    )
  [4] => Array
    (
      [name] => Sally
      [nick_name] => sal
      [availability] => 0
      [is_fav] => 0
    )
)

You can also sort multi-dimensional array for multiple values like as

output:
Array
(
  [0] => Array
    (
      [id] => 1
      [age] => 1
      [sex] => 6
      [name] => a
    )
  [1] => Array
    (
      [id] => 4
      [age] => 2
      [sex] => 1
      [name] => d
    )
  [2] => Array
    (
      [id] => 2
      [age] => 3
      [sex] => 1
      [name] => c
    )
  [3] => Array
    (
      [id] => 3
      [age] => 3
      [sex] => 1
      [name] => b
    )
)

this is a new multisort function for sorting on multiple subfield like it will be in sql : 'ORDER BY field1, field2'
number of sort field is undefined

output:
Array
(
  [0] => Array
    (
      [soc] => 1
      [code] => 1
    )
  [1] => Array
    (
      [soc] => 1
      [code] => 1
    )
  [2] => Array
    (
      [soc] => 1
      [code] => 2
    )
  [3] => Array
    (
      [soc] => 2
      [code] => 1
    )
  [4] => Array
    (
      [soc] => 2
      [code] => 5
    )
  [5] => Array
    (
      [soc] => 3
      [code] => 1
    )
  [6] => Array
    (
      [soc] => 3
      [code] => 2
    )
)

I wrote a wrapper for usort that lets you use something similar to an SQL ORDER BY clause. It can sort arrays of associative arrays and arrays of objects and I think it would work with some hybrid case.
Example of how the function works:

To sort an array of objects you would do something like:
Utility::orderBy($objectAry, 'getCreationDate() DESC, getSubOrder() ASC');
This would sort an array of objects that have methods getCreationDate() and getSubOrder().
Here is the function: 

The easiest way to compare two integers is just to take the second away from the first. For example, say you wanted to sort by an integer property of an object. Your comparison function would look like this:

This works because you don't necessarily have to return -1, 0 or 1, the manual states any integer less than, equal to or greater than 0 is OK.

usort returns null when the sorting function is not (yet) defined. The function has to be defined before usort is called, afterwards doesn't work.

As the manual says, "If two members compare as equal, their order in the sorted array is undefined." This means that the sort used is not "stable" and may change the order of elements that compare equal.
Sometimes you really do need a stable sort. For example, if you sort a list by one field, then sort it again by another field, but don't want to lose the ordering from the previous field. In that case it is better to use usort with a comparison function that takes both fields into account, but if you can't do that then use the function below. It is a merge sort, which is guaranteed O(n*log(n)) complexity, which means it stays reasonably fast even when you use larger lists (unlike bubblesort and insertion sort, which are O(n^2)). 

This function will sort on more then one values, test and have fun

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