This question is intended as a reference for questions about sorting arrays in PHP. It is easy to think that your particular case is unique and worthy of a new question, but most are actually minor variations of one of the solutions on this page.
If your question is closed as a duplicate of this one, please ask for your question to be reopened only if you can explain why it differs markedly from all of the below.
How do I sort an array in PHP?
How do I sort a complex array in PHP?
How do I sort an array of objects in PHP?
For the practical answer using PHP's existing functions see 1., for the academic in-detail answer on sorting algorithms (which PHP's functions implement and which you may need for really, really complex cases), see 2.
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Basic one dimensional arrays
$array = array(3, 5, 2, 8);
Applicable sort functions:
sort
rsort
asort
arsort
natsort
natcasesort
ksort
krsort
The difference between those is merely whether key-value associations are kept (the "a
" functions), whether it sorts low-to-high or reverse ("r
"), whether it sorts values or keys ("k
") and how it compares values ("nat
" vs. normal). See http://php.net/manual/en/array.sorting.php for an overview and links to further details.
Multi dimensional arrays, including arrays of objects
$array = array(
array('foo' => 'bar', 'baz' => 42),
array('foo' => ..., 'baz' => ...),
...
);
If you want to sort $array
by the key 'foo' of each entry, you need a custom comparison function. The above sort
and related functions work on simple values that they know how to compare and sort. PHP does not simply "know" what to do with a complex value like array('foo' => 'bar', 'baz' => 42)
though; so you need to tell it.
To do that, you need to create a comparison function. That function takes two elements and must return 0
if these elements are considered equal, a value lower than 0
if the first value is lower and a value higher than 0
if the first value is higher. That's all that's needed:
function cmp(array $a, array $b) {
if ($a['foo'] < $b['foo']) {
return -1;
} else if ($a['foo'] > $b['foo']) {
return 1;
} else {
return 0;
}
}
Often, you will want to use an anonymous function as the callback. If you want to use a method or static method, see the other ways of specifying a callback in PHP.
You then use one of these functions:
Again, they only differ in whether they keep key-value associations and sort by values or keys. Read their documentation for details.
Example usage:
usort($array, 'cmp');
usort
will take two items from the array and call your cmp
function with them. So cmp()
will be called with $a
as array('foo' => 'bar', 'baz' => 42)
and $b
as another array('foo' => ..., 'baz' => ...)
. The function then returns to usort
which of the values was larger or whether they were equal. usort
repeats this process passing different values for $a
and $b
until the array is sorted. The cmp
function will be called many times, at least as many times as there are values in $array
, with different combinations of values for $a
and $b
every time.
To get used to this idea, try this:
function cmp($a, $b) {
echo 'cmp called with $a:', PHP_EOL;
var_dump($a);
echo 'and $b:', PHP_EOL;
var_dump($b);
}
All you did was define a custom way to compare two items, that's all you need. That works with all sorts of values.
By the way, this works on any value, the values don't have to be complex arrays. If you have a custom comparison you want to do, you can do it on a simple array of numbers too.
sort
sorts by reference and does not return anything useful!
Note that the array sorts in place, you do not need to assign the return value to anything. $array = sort($array)
will replace the array with true
, not with a sorted array. Just sort($array);
works.
Custom numeric comparisons
If you want to sort by the baz
key, which is numeric, all you need to do is:
function cmp(array $a, array $b) {
return $a['baz'] - $b['baz'];
}
Thanks to The PoWEr oF MATH this returns a value < 0, 0 or > 0 depending on whether $a
is lower than, equal to or larger than $b
.
Note that this won't work well for float
values, since they'll be reduced to an int
and lose precision. Use explicit -1
, 0
and 1
return values instead.
Objects
If you have an array of objects, it works the same way:
function cmp($a, $b) {
return $a->baz - $b->baz;
}
Functions
You can do anything you need inside a comparison function, including calling functions:
function cmp(array $a, array $b) {
return someFunction($a['baz']) - someFunction($b['baz']);
}
Strings
A shortcut for the first string comparison version:
function cmp(array $a, array $b) {
return strcmp($a['foo'], $b['foo']);
}
strcmp
does exactly what's expected of cmp
here, it returns -1
, 0
or 1
.
Spaceship operator
PHP 7 introduced the spaceship operator, which unifies and simplifies equal/smaller/larger than comparisons across types:
function cmp(array $a, array $b) {
return $a['foo'] <=> $b['foo'];
}
Sorting by multiple fields
If you want to sort primarily by foo
, but if foo
is equal for two elements sort by baz
:
function cmp(array $a, array $b) {
if (($cmp = strcmp($a['foo'], $b['foo'])) !== 0) {
return $cmp;
} else {
return $a['baz'] - $b['baz'];
}
}
For those familiar, this is equivalent to an SQL query with ORDER BY foo, baz
.
Also see this very neat shorthand version and how to create such a comparison function dynamically for an arbitrary number of keys.
Sorting into a manual, static order
If you want to sort elements into a "manual order" like "foo", "bar", "baz":
function cmp(array $a, array $b) {
static $order = array('foo', 'bar', 'baz');
return array_search($a['foo'], $order) - array_search($b['foo'], $order);
}
For all the above, if you're using PHP 5.3 or higher (and you really should), use anonymous functions for shorter code and to avoid having another global function floating around:
usort($array, function (array $a, array $b) { return $a['baz'] - $b['baz']; });
複雑な多次元配列のソートは、このように簡単に行えます。ここでも、2 つの項目のうちどちらが「大きい」かを判別する方法を PHP に教えるという点だけを考えてください。実際のソートは PHP に任せてください。
また、上記のすべてにおいて、昇順と降順を切り替えるには、引数$a
と$b
引数を入れ替えるだけです。例:
return $a['baz'] - $b['baz']; // ascending
return $b['baz'] - $a['baz']; // descending
ある配列を別の配列に基づいてソートする
そして奇妙なことにarray_multisort
を使用すると、ある配列を別の配列に基づいて並べ替えることができます。
$array1 = array( 4, 6, 1);
$array2 = array('a', 'b', 'c');
ここで期待される結果は次のようになります。
$array2 = array('c', 'a', 'b'); // the sorted order of $array1
そこへ行くには以下を使用しますarray_multisort
:
array_multisort($array1, $array2);
array_column
PHP 5.5.0 以降では、多次元配列から列を抽出し、その列に基づいて配列を並べ替えることができます。
array_multisort(array_column($array, 'foo'), SORT_DESC, $array);
複数の列をそれぞれどちらの方向にも並べ替えることもできます。
array_multisort(array_column($array, 'foo'), SORT_DESC,
array_column($array, 'bar'), SORT_ASC,
$array);
PHP 7.0.0 以降では、オブジェクトの配列からプロパティを抽出することもできます。
より一般的なケースがある場合は、この回答を自由に編集してください。