#### wu-manber-fuzzy-search

An OCaml Implementation of the wu-manber fuzzy search algorithm using `Int63`

from the `optint`

package as the underlying bitvectors.

The library can be used to search for a keyword/pattern in a body of text while

allowing for spelling errors. We use Levenshtein distances as the notion of

spelling errors, and the functions in the library take some error limit `k`

and

searches for substrings in the text with Levenshtein distance less than `k`

from

the pattern.

## Wu and Manber variants

I use the shift-or variant of the algorithm to save some bitwise operations.

This is also called the `bitap`

algorithm, and the shift-or version was

originally introduced by Baeza-Yates and Gonnet.

Even for the shift-or version, I provide two variants of the algorithm.

The original version from Wu and Manber's technical report.

A right-leaning variant, where delete edits are skipped at the end of the

pattern unless at the very end of text. This reports better edit distances is

some circumstances.

The right-leaning variant is guaranteed to find a match if and only if the

original algorithm finds a match, and the error count reported by the variant is

guaranteed to be no worse than the original.

But the variant is a little harder to use since extra work is needed to check

for matches at the end of the text.

## Documentation

The documentation for the library can be found

here.

## Examples

```
# #require "wu-manber-fuzzy-search";;
# open Wu_Manber;;
# StringSearch.(search ~k:2 ~pattern:"abcd" ~text:"abcd" |> report);;
- : string = "Pattern matched with 2 errors at character 2 of text"
# StringSearch.(search ~k:2 ~pattern:"abcd" ~text:"abd" |> report);;
- : string = "Pattern matched with 2 errors at character 2 of text"
# StringSearch.(search_right_leaning ~k:2 ~pattern:"abcd" ~text:"abcd" |> report);;
- : string = "Pattern matched with 0 errors at character 4 of text"
# StringSearch.(search_right_leaning ~k:2 ~pattern:"abcd" ~text:"abd" |> report);;
- : string = "Pattern matched with 1 errors at character 3 of text"
```

## Limits

The library only supports patterns of length 63. This is unlikely to be extended

any time soon.

## Runtime and Space Requirements

To search with an edit distance `k`

, we need to track of an array of `Int63.t`

of size `k+1`

. To process a character in the text, we usually need around `6`

bitwise operations for every element of the array.

The high-level apis also use some matcher objects, these store patterns, arrays,

or hashtables which require additional space.

## Reference

The shift-and version of the algorithm is described in S. Wu and U. Manber, Fast

Text Searching With Errors, tech. rep. TR 91-11, University of Arizona, 1991.

The shift-or version is described in the Wikipedia article for Bitap

Algorithm.

## Related packages

`agrep`

implements the shift-and

version, but much of it is implmented in C.

There's also the main `agrep`

unix tool tool itself by Manber and Wu.

## Future Work

PRs are welcome, as long as you are understand that you would be releasing your

code under CC0.

Here are extensions that I would like to have in the future.

Add versions of the algorithm that mutate an array instead of creating new

arrays all the time.Add specialized versions for exact matches and small error limits.

Support multi-match and limited expressions.

Full Regular Expressions Support.

Support Demarau-Levenshtein distances.

Support long patterns.

The limited expressions support should not be too difficult, but I haven't

thought about if the right-leaning variant has weird interactions with limited

expressions.

sha256=6383ed484151c85bd4de90592391d9117c9ea03eddc04bef0af5cfe57b25f56f

sha512=6d6aae059225726a24ad44eb1a47d90507d9c9a429be41a9c577baf01d29c63d7dd3bc5767602cc4dfb21d28f296ea4000f7a9b91a3e50740c85b02771f66a95

with-doc

>= "1.0.0" & with-test

>= "0.1.0"

>= "4.10.0"

>= "2.8"