lexical-sort

This is a library to compare and sort strings (or file paths) lexicographically. This means that non-ASCII characters such as á or ß are treated like their closest ASCII character: á is treated as a, ß is treated as ss, etc.

The comparison is case-insensitive. Alphanumeric characters are sorted after all other characters (punctuation, whitespace, special characters, emojis, ...).

It is possible to enable natural sorting, which also handles ASCII numbers. For example, 50 is less than 100 with natural sorting turned on. It's also possible to skip characters that aren't alphanumeric, so e.g. f-5 is next to f5.

If different strings have the same ASCII representation (e.g. "Foo" and "fóò"), it falls back to the default method from the standard library, so sorting is deterministic.

Usage

To sort strings or paths, you can use the LexicalSort trait:

use lexical_sort::LexicalSort;

let mut strings = vec!["ß", "é", "100", "hello", "world", "50", ".", "B!"];

strings.lexical_sort(/* enable natural sorting: */ true);
assert_eq!(&strings, &[".", "50", "100", "B!", "é", "hello", "ß", "world"]);

To just compare two strings, use the natural_cmp, lexical_cmp, lexical_natural_cmp, lexical_cmp_only_alnum or lexical_natural_cmp_only_alnum function.

Characteristics

The comparison functions constitute a total order. Two strings are only considered equal if they consist of exactly the same Unicode code points.

Performance

The algorithm uses iterators and never allocates memory on the heap. It is optimized for strings that consist mostly of ASCII characters; for ASCII-only strings, the lexicographical comparison functions are only 2 to 3 times as slow as the default method from std, which just compares Unicode code points.

Note that comparisons are slower for strings where many characters at the start are the same (after transliterating them to lowercase ASCII).

Benchmarks

These benchmarks were executed on an AMD A8-7600 Radeon R7 CPU with 4x 3.1GHz.

The benchmark on the left sorts 100 randomly generated strings with 5 to 20 characters, containing both ASCII and non-ASCII characters. Several of them need to be transliterated to multiple characters (e.g. ß, æ).

The benchmark in the middle also sorts 100 randomly generated strings with 5 to 20 characters, but they are ASCII-only.

The benchmark on the right sorts 100 randomly generated strings. Each string consists of "T-" followed by 1 to 8 decimal digits. This is a stress test for natural sorting.

Contributing

Contributions, bug reports and feature requests are welcome!

If support for certain characters is missing, you can contribute them to the any_ascii crate.

Let me know if you want to use this in no_std. It's certainly possible to add no_std support to this crate and its dependencies.

License

This project is dual-licensed under the MIT and Apache 2.0 license. Use whichever you prefer.