To sort multidimensional PHP arrays by specific keys, use the usort() function. 1. Use usort() with a custom comparison function to achieve sorting through the spaceship operator or traditional comparison method; 2. If you want to sort in descending order, just change the comparison value; 3. It can be encapsulated into a reusable function to support different keys and sorting directions. For example, sort_by_key($people, 'age') can be sorted in ascending order of age.
Sorting a multidimensional PHP array by a specific key isn't something you can do directly with basic sorting functions like sort() or asort() , because those don't handle nested arrays. But there's a straightforward way to do it using built-in PHP functions — mainly usort() .
Here's how to do it.
Use usort() with a custom comparison function
The main tool for sorting multidimensional arrays by a specific key is usort() . It allows you to define your own logic for comparing elements in the array.
For example, if you have an array like this:
$people = [
['name' => 'John', 'age' => 25],
['name' => 'Jane', 'age' => 30],
['name' => 'Doe', 'age' => 20]
]; And you want to sort it by the 'age' key, you can do:
usort($people, function($a, $b) {
return $a['age'] <=> $b['age'];
}); This uses the spaceship operator ( <=> ), which simplifies comparisons:
- Returns -1 if the left side is smaller
- Returns 0 if equal
- Returns 1 if the left side is larger
If you're using an older version of PHP (before 7), you'll need to write out the full comparison:
usort($people, function($a, $b) {
if ($a['age'] == $b['age']) return 0;
return ($a['age'] < $b['age']) ? -1 : 1;
});Sorting in descending order
To reverse the order (eg, sort from highest to lowest age), just flip the comparison values:
usort($people, function($a, $b) {
return $b['age'] <=> $a['age'];
});Or, if you're not using the spaceship operator:
usort($people, function($a, $b) {
if ($b['age'] == $a['age']) return 0;
return ($b['age'] < $a['age']) ? -1 : 1;
});This gives you full control over the direction of the sort.
Reusable function for different keys
If you find yourself doing this often, it might be useful to create a reusable helper function that takes the array and the key as parameters:
function sort_by_key(&$array, $key) {
usort($array, function($a, $b) use ($key) {
return $a[$key] <=> $b[$key];
});
}Then you can simply call:
sort_by_key($people, 'age');
You could even extend this function to support descending order or other data types if needed.
That's basically it.
It's not complicated once you get used to using usort() , but it's easy to forget exactly how the comparison function works — especially if you're switching between languages ??or haven't worked with callbacks much. Just remember: define the logic inside usort() using either the spaceship operator or a traditional if/return structure, depending on your PHP version.
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