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What is an array in PHP and what types of arrays does PHP support? How do you add, remove, and access elements within a PHP array? How do array_map, array_filter, and array_reduce help you transform and process array data without writing manual loops? What is array destructuring in PHP, and how does the list function or short array syntax simplify extracting values from an array? How do you merge, combine, and compare arrays in PHP, and what are the subtle differences between array_merge and the plus operator? How does PHP handle array copying behavior, and when do arrays actually get passed by reference instead of by value?
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How do you sort arrays in PHP, and what is the difference between functions like sort, asort, and usort?

Intermediate

Answer

The sort function reorders an array by value and reindexes the keys numerically, asort sorts an array by value while preserving the original keys, which is useful for associative arrays, and usort lets you define a completely custom comparison function to sort elements based on any logic you need, such as sorting an array of objects by a specific property.
$scores = ['Ali' => 85, 'Sara' => 92, 'Omar' => 78];
asort($scores);

$products = [['name' => 'Pen', 'price' => 5], ['name' => 'Book', 'price' => 20]];
usort($products, fn($a, $b) => $a['price'] <=> $b['price']);
Real-world example An e commerce catalog uses usort with a custom comparison function to sort a list of products by price, letting customers view items from cheapest to most expensive.

Common follow-ups: What does the spaceship operator do in a usort comparison function?;How do you sort an array in descending order?

Functions & Scope;OOP
All 7 Arrays in PHP questions