`Sort`

Arrays in PHP are a powerful type with both keys and values. But they have ordering and we can thus sort them—a variety of helpful sort() functions are available.

The sorting functions in this language have versions with different leading characters. For example, for a user-defined function sort(), we have usort().

Example

Here we see four different sorting functions. We first use sort(), which is an ascending (low to high) sort that is probably the most commonly-used one.

Step 1 We sort a four-element array that we declared with short array syntax. It has strings, so we get "a" before "z".

Step 2 We use usort() for a user-defined sort. We specify an inline function that returns 0, -1 or 1 based on how any two elements are ordered.

Step 3 For a key-based sort, we invoke ksort(). This acts upon the keys in an array.

Step 4 The rsort() function is a reverse sort. It both sorts and then reverses—it does not just reverse the ordering of the elements.

// Part 1: Default sort.
$values = ["z", "b", "y", "a"];
sort($values);
print_r($values);

// Part 2: Use usort for user-defined sort.
//         Specify an inline function for comparison.
$values = ["aa", "bbb", "c"];
usort($values, function ($a, $b) {
    if (strlen($a) == strlen($b)) {
        return 0;
    }
    return strlen($a) < strlen($b) ? -1 : 1;
});
print_r($values);

// Part 3: Sort based on a key.
$values = array(2 => "a", 10 => "b", 0 => "c");
ksort($values);
print_r($values);

// Part 4: Reverse sort.
$values = [10, 50, 0];
rsort($values);
print_r($values);Array
(
    [0] => a
    [1] => b
    [2] => y
    [3] => z
)
Array
(
    [0] => c
    [1] => aa
    [2] => bbb
)
Array
(
    [0] => c
    [2] => a
    [10] => b
)
Array
(
    [0] => 50
    [1] => 10
    [2] => 0
)

`Comparison` function notes

Consider the usort() function again. It requires a comparison function that receives 2 arguments, and returns 0, -1 or 1.

Note For two items that are equal in sorting order, the value 0 must be returned.

And If the first argument should come before the second, we return -1, and if after, we return 1.

Sorting a, b:

a same as b:  0
a before b:  -1
a after b:    1

Using the simplest sorting function that works is usually the best choice. For example, if sort() will work, using this function will lead to the clearest, most understandable code.

Sort

Example

Comparison function notes

`Sort`

`Comparison` function notes