natcasesort()

Introduction

natcasesort() sorts an array using a natural order algorithm with a case-insensitive comparison. "Natural order" means it orders strings the way a human would — so img10 comes after img2, not before it like a plain alphabetical sort would do.

This page covers what natural ordering is, how natcasesort() differs from natsort() and sort(), and the gotchas around keys and return values.

Syntax

natcasesort(array &$array): bool

It takes the array by reference, sorts it in place, and returns true on success. You do not assign the result back — the array you pass in is modified directly.

Why natural order matters

A regular alphabetical sort compares strings character by character, so "img10" sorts before "img2" because 1 is less than 2. That is rarely what a person expects when filenames or labels contain numbers. Natural order treats the digit runs as numbers, giving the human-friendly result.

Basic example

Output:

Array
(
    [3] => Boston
    [2] => Chicago
    [1] => Los Angeles
    [0] => New York
    [4] => San Francisco
)

Notice the keys (3, 2, 1, 0, 4) are not renumbered — each value keeps its original key. If you need keys reset to 0, 1, 2…, use sort() instead, or run the result through array_values().

natcasesort() vs natsort() vs sort()

The difference between these three is easiest to see with mixed-case strings that contain numbers:

<?php

$files = array("IMG10.png", "img12.png", "img2.png", "IMG1.png", "img10.png");

$a = $files;
natcasesort($a);   // natural + case-insensitive
print_r($a);

Output:

Array
(
    [3] => IMG1.png
    [2] => img2.png
    [0] => IMG10.png
    [4] => img10.png
    [1] => img12.png
)

With natsort() (case-sensitive) the same data sorts differently, because uppercase letters compare lower than lowercase ones — so IMG10 lands before img2:

Array
(
    [3] => IMG1.png
    [0] => IMG10.png
    [2] => img2.png
    [4] => img10.png
    [1] => img12.png
)

And sort() (regular, not natural) reindexes the keys and puts img10/img12 before img2:

Array
(
    [0] => IMG1.png
    [1] => IMG10.png
    [2] => img10.png
    [3] => img12.png
    [4] => img2.png
)

Use natcasesort() when the order should match human intuition and case should be ignored — for example listing user-uploaded filenames where someone may have typed IMG or img.

Gotchas

• It returns a bool, not the sorted array. $sorted = natcasesort($arr); sets $sorted to true, not your data. The data is in $arr.
• Keys are preserved. This breaks code that assumes 0-based keys afterwards. Wrap with array_values($arr) if you need a clean list.
• Non-string values are compared as strings. Numbers, booleans, etc. are cast to strings before comparison.

Related functions

• natsort() — natural order, case-sensitive.
• sort() — regular ascending sort, reindexes keys.
• asort() — ascending sort that preserves keys (not natural).
• usort() — sort with your own comparison callback.

Available since PHP 4.0.0.

Practice