How to Sort a Multi-Dimensional Array in PHP by a Specific Key?

Sorting Multi-Dimensional Arrays by a Specific Key

Sorting multi-dimensional arrays by a specific key value can be achieved using various methods in PHP. Let's explore a common problem and its solutions using this technique.

Problem:

How do we sort an array based on the "order" key?

Array's Structure:

$myArray = [
    [
        'hashtag' => 'a7e87329b5eab8578f4f1098a152d6f4',
        'title'   => 'Flower',
        'order'   => 3
    ],
    [
        'hashtag' => 'b24ce0cd392a5b0b8dedc66c25213594',
        'title'   => 'Free',
        'order'   => 2
    ],
    [
        'hashtag' => 'e7d31fc0602fb2ede144d18cdffd816b',
        'title'   => 'Ready',
        'order'   => 1
    ]
];

Solutions:

1. Using usort with a Custom Function:

This method involves defining a custom sorting function that compares the "order" values and returns an appropriate comparison result.

function sortByOrder($a, $b) {
    if ($a['order'] > $b['order']) {
        return 1;
    } elseif ($a['order'] < $b['order']) {
        return -1;
    }
    return 0;
}

usort($myArray, 'sortByOrder');

2. Using Anonymous Functions:

In PHP 5.3 and later, anonymous functions can be used to simplify the custom sorting function.

usort($myArray, function($a, $b) {
    if ($a['order'] > $b['order']) {
        return 1;
    } elseif ($a['order'] < $b['order']) {
        return -1;
    }
    return 0;
});

3. Using the Spaceship Operator (PHP 7 and later):

PHP 7 introduced the spaceship operator (< =>) for concise comparison operations.

usort($myArray, function($a, $b) {
    return $a['order'] <=> $b['order'];
});

4. Using Arrow Functions (PHP 7.4 and later):

Arrow functions further simplify code by eliminating the function keyword.

usort($myArray, fn($a, $b) => $a['order'] <=> $b['order']);

Multi-Dimensional Sorting:

For arrays with nested structures, you can extend the sorting function to consider multiple keys. This allows for complex sorting, such as sorting by "order" within "suborder."

usort($myArray, function($a, $b) {
    $retval = $a['order'] <=> $b['order'];
    if ($retval == 0) {
        $retval = $a['suborder'] <=> $b['suborder'];
        if ($retval == 0) {
            $retval = $a['details']['subsuborder'] <=> $b['details']['subsuborder'];
        }
    }
    return $retval;
});

Note: If you need to maintain key associations, consider using uasort() instead of usort().

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