How to sort multiple arrays or multidimensional arrays using the array_multisort function?

array_multisort() can be used to sort multiple arrays at one time, or to sort multidimensional arrays according to a certain dimension or multiple dimensions.

array_multisort — Sort multiple arrays or multidimensional arrays
Description
bool array_multisort (array ar1 [, mixed arg [, mixed ... [, array ...]]] )
array_multisort
(PHP 4, PHP 5)
Returns TRUE if successful, returns FALSE if failed.
array_multisort() can be used to sort multiple arrays at once, or to sort multi-dimensional arrays according to one or more dimensions.
Associated (string) key names remain unchanged, but numeric key names will be re-indexed.
The input array is treated as a table column and sorted by row - this is similar to the functionality of SQL's ORDER BY clause. The first array is the main array to be sorted. If the rows (values) in the array are compared to be the same, they are sorted according to the size of the corresponding value in the next input array, and so on.
The parameters of this function are somewhat unusual in structure, but very flexible. The first parameter must be an array. Each of the following parameters can be an array or a sort flag listed below.

Sort order flags:
SORT_ASC – Sort in ascending order

SORT_DESC – Sort in descending order
Sort type flags:
SORT_REGULAR – Sort Items are compared according to the usual method

SORT_NUMERIC – items are compared according to numeric values

SORT_STRING – items are compared according to strings
Cannot specify two similar items after each array sorting flag. The sort flags specified after each array are valid only for that array – before that the default values ​​SORT_ASC and SORT_REGULAR were used.

Example 1. Sort multiple arrays

<?php 
$ar1 = array(“10″, 100, 100, “a”); 
$ar2 = array(1, 3, “2″, 1); 
array_multisort($ar1, $ar2); 
var_dump($ar1); 
var_dump($ar2); 
?>

After sorting in this example, the first array will contain "10", "a" ,100,100. The second array will contain 1,1,"2",3. The order of the items in the second array is exactly the same as the order of the corresponding items (100 and 100) in the first array.

array(4) { 
[0]=> string(2) “10″ 
[1]=> string(1) “a” 
[2]=> int(100) 
[3]=> int(100) 
} 
array(4) { 
[0]=> int(1) 
[1]=> int(1) 
[2]=> string(1) “2″ 
[3]=> int(3) 
}

Example 2. Sorting multi-dimensional arrays

<?php 
$ar = array (array (“10″, 100, 100, “a”), array (1, 3, “2″, 1)); 
array_multisort ($ar[0], SORT_ASC, SORT_STRING, 
$ar[1], SORT_NUMERIC, SORT_DESC); 
?>

After sorting in this example, the first array will contain 10, 100, 100, "a" ( As strings sorted ascending), the second array will contain 1, 3, "2", 1 (as numeric sorting descending).
Example 3. Sorting multi-dimensional array

<?php 
$ar = array( 
array(“10″, 11, 100, 100, “a”), 
array( 1, 2, “2″, 3, 1) 
); 
array_multisort($ar[0], SORT_ASC, SORT_STRING, 
$ar[1], SORT_NUMERIC, SORT_DESC); 
var_dump($ar); 
?>

In this example, after sorting, the first array will become "10", 100, 100, 11, "a" (being treated as strings in ascending order). The second array will contain 1, 3, “2″, 2, 1 (treated as numbers in descending order).

array(2) { 
[0]=> array(5) { 
[0]=> string(2) “10″ 
[1]=> int(100) 
[2]=> int(100) 
[3]=> int(11) 
[4]=> string(1) “a” 
} 
[1]=> array(5) { 
[0]=> int(1) 
[1]=> int(3) 
[2]=> string(1) “2″ 
[3]=> int(2) 
[4]=> int(1) 
} 
}

Example 4. Sort database results
In this example, each cell in the data array represents a row in a table. This is a typical collection of data recorded in a database.
The data in the example is as follows:
volume | edition
——-+——–
67 | 2
86 | 1
85 | 6
98 | 2
86 | 6
67 | 7
The data are all stored in an array named data. This is usually obtained from the database through a loop, such as mysql_fetch_assoc().

<?php 
$data[] = array(‘volume&#39; => 67, ‘edition&#39; => 2); 
$data[] = array(‘volume&#39; => 86, ‘edition&#39; => 1); 
$data[] = array(‘volume&#39; => 85, ‘edition&#39; => 6); 
$data[] = array(‘volume&#39; => 98, ‘edition&#39; => 2); 
$data[] = array(‘volume&#39; => 86, ‘edition&#39; => 6); 
$data[] = array(‘volume&#39; => 67, ‘edition&#39; => 7); 
?>

In this example, volume will be sorted in descending order and edition will be sorted in ascending order.
Now we have an array containing rows, but array_multisort() requires an array containing columns, so use the following code to get the columns and then sort them.

<?php 
// 取得列的列表 
foreach ($data as $key => $row) { 
$volume[$key] = $row[&#39;volume&#39;]; 
$edition[$key] = $row[&#39;edition&#39;]; 
} 
// 将数据根据 volume 降序排列，根据 edition 升序排列 
// 把 $data 作为最后一个参数，以通用键排序 
array_multisort($volume, SORT_DESC, $edition, SORT_ASC, $data); 
?>

The data collection is now sorted, and the results are as follows:

volume | edition
——-+——–
98 | 2
86 | 1
86 | 6
85 | 6
67 | 2
67 | 7

Example 5. Case-insensitive alphabetical sorting
SORT_STRING and SORT_REGULAR are both distinctions For uppercase and lowercase letters, uppercase letters will be sorted before lowercase letters.
To perform case-insensitive sorting, you must sort by a copy of the lowercase letters of the original array.

<?php 
$array = array(‘Alpha&#39;, ‘atomic&#39;, ‘Beta&#39;, ‘bank&#39;); 
$array_lowercase = array_map(&#39;strtolower&#39;, $array); 
array_multisort($array_lowercase, SORT_ASC, SORT_STRING, $array); 
print_r($array); 
?>

The above example will output:

Array 
( 
[0] => Alpha 
[1] => atomic 
[2] => bank 
[3] => Beta 
)

补充资料:
对于PHP语言中的多维数组排序时最为复杂的一个排序方式。我们在实际编码中将会用到PHP函数array_multisort()来实现这一复杂的排序。例如，首先对一个嵌套数组使用一个普通的关键字进行排序，然后再根据另一个关键字进行排序。这与使用SQL的ORDER BY语句对多个字段进行排序非常相似。
PHP函数asort()利用值排序的具体方式解析
PHP函数arsort()的功能特点详解
PHP自然语言排序的特点介绍
PHP自然语言倒序的具体实现方式
如何运用PHP函数usort()实现自定义排序
Listing J示例为我们具体说明了PHP函数array_multisort()的工作方式：
1, "name" => "Boney M", "rating" => 3), array("id" => 2, "name" => "Take That", "rating" => 1), array("id" => 3, "name" => "The Killers", "rating" => 4), array("id" => 4, "name" => "Lusain", "rating" => 3), ); foreach ($data as $key => $value) { $name[$key] = $value[name]; $rating[$key] = $value[rating]; } array_multisort($rating, $name, $data); print_r($data);?> 这里，我们在$data数组中模拟了一个行和列数组。然后，我使用PHP函数array_multisort()对数据集合进行重排，首先是根据rating进行排序，然后，如果rating相等的话，再根据name排序。它的输出结果如下：

Array ([0] => Array 
( 
[id] => 2 
[name] => Take That 
[rating] => 1 
) [1] => Array 
( 
[id] => 1 
[name] => Boney M 
[rating] => 3 
) 
[2] => Array 
( 
[id] => 4 
[name] => Lusain 
[rating] => 3 
) 
[3] => Array 
( 
[id] => 3 
[name] => The Killers 
[rating] => 4 
) 
)

PHP函数array_multisort()是PHP中最有用的函数之一，它有非常广泛的应用范围。另外，就如你在例子中所看到的，它能对多个不相关的数组进行排序，也可以使用其中的一个元素作为下次排序的基础，还可以对数据库结果集进行排序。

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