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).

Sorting function attributes
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