php数组排序

• sort() - 以升序对数组排序
• rsort() - 以降序对数组排序
• asort() - 根据值，以升序对关联数组进行排序
• arsort() - 根据值，以降序对关联数组进行排序
• ksort() - 根据键，以升序对关联数组进行排序
• krsort() - 根据键，以降序对关联数组进行排序

以sort为例

<?php 
$colors = array("red" => "b1","green" => "c2","blue" => "d3","yellow" => "a4"); 
var_dump($colors);
sort($colors);
var_dump($colors);
?>

执行结果如下

array(4) {
  ["red"]=>
  string(2) "b1"
  ["green"]=>
  string(2) "c2"
  ["blue"]=>
  string(2) "d3"
  ["yellow"]=>
  string(2) "a4"
}
array(4) {
  [0]=>
  string(2) "a4"
  [1]=>
  string(2) "b1"
  [2]=>
  string(2) "c2"
  [3]=>
  string(2) "d3"
}

即 sort和rsort在进行数组排序时根据数组的value，按照字母表a~z的顺序进行排序 ，排序后的数组的key值会强制变为0,1,2,3... ，原数组value不全为字母时，sort以及rsort会从第一位开始往后寻找字母进行排序，如若原数组的value不含a~z 如下

<?php 
$colors = array("red" => "4","green" => "2","blue" => "3","yellow" => "1"); 
var_dump($colors);
sort($colors);
var_dump($colors);
?>

执行结果

array(4) {
  ["red"]=>
  string(1) "4"
  ["green"]=>
  string(1) "2"
  ["blue"]=>
  string(1) "3"
  ["yellow"]=>
  string(1) "1"
}
array(4) {
  [0]=>
  string(1) "1"
  [1]=>
  string(1) "2"
  [2]=>
  string(1) "3"
  [3]=>
  string(1) "4"
}

sort和rsort会按照数字的大小进行排序 key值也会强制转换成0,1,2,3.....

asort和arsort
根据value进行升序/降序，看起来跟sort和rsort一样，但是sort和rsort的排序会重置原先的key值，变成0,1,2,3...，而asort和arsort并不会 其他规则一样 如下

<?php 
$colors = array("red" => "4","green" => "2","blue" => "3","yellow" => "1"); 
var_dump($colors);
asort($colors);
var_dump($colors);
?>

执行结果

array(4) {
  ["red"]=>
  string(1) "4"
  ["green"]=>
  string(1) "2"
  ["blue"]=>
  string(1) "3"
  ["yellow"]=>
  string(1) "1"
}
array(4) {
  ["yellow"]=>
  string(1) "1"
  ["green"]=>
  string(1) "2"
  ["blue"]=>
  string(1) "3"
  ["red"]=>
  string(1) "4"
}

ksort以及krsrot示例

<?php 
$colors = array("red" => "4","green" => "2","blue" => "3","yellow" => "1"); 
var_dump($colors);
ksort($colors);
var_dump($colors);
?>

执行结果

array(4) {
  ["red"]=>
  string(1) "4"
  ["green"]=>
  string(1) "2"
  ["blue"]=>
  string(1) "3"
  ["yellow"]=>
  string(1) "1"
}
array(4) {
  ["blue"]=>
  string(1) "3"
  ["green"]=>
  string(1) "2"
  ["red"]=>
  string(1) "4"
  ["yellow"]=>
  string(1) "1"
}