Sorting Arrays
PHP has several functions that deal with sorting arrays, and this document exists to help sort it all out.
The main differences are:
- Some sort based on the array keys, whereas others by the values: $array['key'] = 'value';
- Whether or not the correlation between the keys and values are maintained after the sort, which may mean the keys are reset numerically (0,1,2 ...)
- The order of the sort: alphabetical, low to high (ascending), high to low (descending), numerical, natural, random, or user defined
- Note: All of these sort functions act directly on the array variable itself, as opposed to returning a new sorted array
- If any of these sort functions evaluates two members as equal then the order is undefined (the sorting is not stable).
| Function name | Sorts by | Maintains key association | Order of sort | Related functions |
|---|---|---|---|---|
| array_multisort() | value | associative yes, numeric no | first array or sort options | array_walk() |
| asort() | value | yes | low to high | arsort() |
| arsort() | value | yes | high to low | asort() |
| krsort() | key | yes | high to low | ksort() |
| ksort() | key | yes | low to high | asort() |
| natcasesort() | value | yes | natural, case insensitive | natsort() |
| natsort() | value | yes | natural | natcasesort() |
| rsort() | value | no | high to low | sort() |
| shuffle() | value | no | random | array_rand() |
| sort() | value | no | low to high | rsort() |
| uasort() | value | yes | user defined | uksort() |
| uksort() | key | yes | user defined | uasort() |
| usort() | value | no | user defined | uasort() |
Коментарии
Another way to do a case case-insensitive sort by key would simply be:
<?php
uksort($array, 'strcasecmp');
?>
Since strcasecmp is already predefined in php it saves you the trouble to actually write the comparison function yourself.
While this may seem obvious, user-defined array sorting functions ( uksort(), uasort(), usort() ) will *not* be called if the array does not have *at least two values in it*.
The following code:
<?php
function usortTest($a, $b) {
var_dump($a);
var_dump($b);
return -1;
}
$test = array('val1');
usort($test, "usortTest");
$test2 = array('val2', 'val3');
usort($test2, "usortTest");
?>
Will output:
string(4) "val3"
string(4) "val2"
The first array doesn't get sent to the function.
Please, under no circumstance, place any logic that modifies values, or applies non-sorting business logic in these functions as they will not always be executed.