Sorting Arrays in PHP: sort, asort, ksort

Sorting arrays is one of the most common operations in PHP programming. It lets you order data by values or keys, which is essential in reports, product lists, rankings, filtering results, or preparing data for display in a user interface. In this lesson, you’ll learn how sorting works with PHP functions: sort, asort, and ksort. You’ll see practical code examples, best practices, and the most common mistakes to avoid.

Basics of Array Sorting in PHP

What you need to know first

• Indexed arrays have numeric indexes (0, 1, 2, ...).
• Associative arrays have string keys (e.g., "name" => "Alice").
• PHP provides different sorting functions:

All these functions:

• Work in place (modify the original array).
• Return a boolean (true on success).
• Can take additional sorting flags such as SORTNUMERIC, SORTSTRING, SORTNATURAL, SORTFLAGCASE.

<?php
$numbers = [5, 2, 9, 1, 2];

sort($numbers); // sorts ascending and reindexes
print_r($numbers); // [1, 2, 2, 5, 9]

<?php
$data = ["10", "2", "Ananas", "banana"];

// Default sorting (SORT_REGULAR):
sort($data);
print_r($data);
// "10" and "2" are strings, compared lexicographically ("10" < "2").

// Force numeric sorting:
$data = ["10", "2", "30"];
sort($data, SORT_NUMERIC);
print_r($data); // ["2", "10", "30"]

// Force string sorting (case-insensitive):
$fruits = ["banana", "Ananas", "plum"];
sort($fruits, SORT_STRING | SORT_FLAG_CASE);
print_r($fruits); // ["Ananas", "banana", "plum"]

<?php
$files = ["file10.txt", "file2.txt", "file1.txt"];
natsort($files); // natural value sorting, preserves keys
print_r($files);

<?php
$ages = [
    "Alice" => 25,
    "Olek"  => 19,
    "Zenek" => 19,
    "Bartek"=> 30,
];

asort($ages);
print_r($ages);
/*
Result:
[
    "Olek"  => 19,
    "Zenek" => 19,
    "Alice" => 25,
    "Bartek"=> 30,
]
*/

<?php
arsort($ages);
print_r($ages);

<?php
$scores = ["Alice" => "10", "Olek" => "2", "Bartek" => "30"];
asort($scores, SORT_NUMERIC);
print_r($scores);

<?php
$settings = [
    "db_host" => "localhost",
    "app_env" => "prod",
    "cache"   => true,
];

ksort($settings);
print_r($settings);

<?php
$data = ["10" => "X", "2" => "Y", "1" => "Z"];

ksort($data);
print_r($data); // "1","10","2" (lexicographic)

ksort($data, SORT_NUMERIC);
print_r($data); // 1,2,10

<?php
krsort($settings);
print_r($settings);

• Preserve the original if needed:

• Remember PHP 8+: sorting is stable (equal values keep original order).
• For proper language rules (like Polish characters), use intl’s Collator::sort/asort.

Common Mistakes

• Losing keys with sort/rsort (use asort/arsort instead).
• Wrong comparison mode: "10" vs "2" as strings → lexicographic order.
• Mixing value types: numbers + strings may behave unexpectedly.
• Assuming sort returns a sorted array (it returns bool, modifies in place).
• Overcomplicating with usort when flags suffice.

Additional Examples

Natural sort, case-insensitive:

<?php
$files = ["File10.txt", "file2.txt", "file1.txt"];
natcasesort($files);
print_r($files);

Sort keys numerically:

<?php
$map = ["2" => "B", "10" => "C", "1" => "A"];
ksort($map, SORT_NUMERIC);
print_r($map);

Multi-stage sorting (thanks to stability):

<?php
$products = [
    ["name" => "Bananas", "price" => 5],
    ["name" => "Ananas",  "price" => 5],
    ["name" => "Plums",   "price" => 7],
];

usort($products, fn($a,$b) => $a["name"] <=> $b["name"]);
usort($products, fn($a,$b) => $a["price"] <=> $b["price"]);
print_r($products);

Summary

• sort – sorts by values, reindexes (loses keys).
• asort – sorts by values, keeps keys (best for associative arrays).
• ksort – sorts by keys.
• Use correct flags: SORTNUMERIC, SORTSTRING, SORTNATURAL.
• Sorting modifies arrays in place, returns bool.
• Beware mixed types, key preservation, and misunderstanding return values.
• For locale-aware sorting: use intl’s Collator.

• Which function sorts associative array by values and keeps keys? → asort
• Which flag for numeric-like strings? → SORTNUMERIC
• What does ksort do? → Sorts by keys, preserves values
• How to sort \["file2","file10","file1"] naturally? → natsort
• Does sort() return the sorted array? → No (returns bool, sorts in place)
• How to sort associative array by keys descending? → krsort

Now you know the essentials of sorting arrays in PHP. Practice with different flags and data types to gain confidence using sort, asort, and ksort effectively.