Sort 2d array (with inconsistent column names) by first column

Question

How can I sort an array or rows by the first value in each row?

$array = [
    ['item1' => 80],
    ['item2' => 25],
    ['item3' => 85],
];

Desired output:

[
    ['item2' => 25],
    ['item1' => 80],
    ['item3' => 85],
]

Answer 1

You need to use usort, a function that sorts arrays via a user defined function. Something like:

usort(
    $yourArray, 
    fn(array $a, array $b): int /* (1),(2) range: -1 ... 1 */
    => reset($a) /* get the first array elements from $a */ 
       <=>  /* (3) <--- the spaceship operator */
       reset($b) /* and from $b for comparison */
);

1. fn (...) => ... Arrow Functions (PHP 7.4)
2. function name (): int Return type declarations (PHP 7.0)
3. <=> Spaceship Operator (PHP 7.0)

(see it live on 3v4l.org)

---

Expressed in older, well-aged PHP:

function cmp($a, $b)
{
    $a = reset($a); // get the first array elements
    $b = reset($b); // for comparison.
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
}

usort($yourArray, "cmp")

(see it live on 3v4l.org)

Compare this with the answer of one of the questions duplicates.

---

Answer 2

You need to use usort

$array = array (
  0 =>
  array (
    'item1' => 80,
  ),
  1 =>
  array (
    'item2' => 25,
  ),
  2 =>
  array (
    'item3' => 85,
  ),
);

function my_sort_cmp($a, $b) {
    reset($a);
    reset($b);
    return current($a) < current($b) ? -1 : 1;
}

usort($array, 'my_sort_cmp');

print_r($array);

Output:

(
    [0] => Array
        (
            [item2] => 25
        )

    [1] => Array
        (
            [item1] => 80
        )

    [2] => Array
        (
            [item3] => 85
        )

)

Answer 3

With modern PHP, call usort() with the syntactic sugary goodness of an arrow function and the spaceship operator. Access the first element of each row with current() or reset().

Code: (Demo)

usort($array, fn($a, $b) => current($a) <=> current($b));

The equivalent with fewer total function calls: (Demo)

array_multisort(array_map('current', $array), $array);