oluies / scala-aho-corasick

A reasonably efficient implementation of Aho-Corasick in Scala

A reasonably efficient implementation of Aho-Corasick in Scala

This is an imperative implementation of the Aho-Corasick string-matching algorithm written entirely in Scala. It is reasonably efficient, and is character-oriented rather than byte-oriented.

Usage

It is extremely easy to use the library since basically all it does is find matching strings in an input document. There are two ways to use the builder, either using the factory constructor that takes in a Seq example:

import com.corruptmemory.aho_corasick.AhoCorasickBuilder

val builder = AhoCorasickBuilder[Unit](List(("he",()),("she",()),("his",()),("hers",()),("her",())))
val finder = builder.build()

val results = finder.find("Several ushers rushed over to aid her in finding a seat.")
// => Vector(Match(10,he,he,()), Match(9,she,she,()), Match(10,her,her,()), Match(10,hers,hers,()), Match(18,he,he,()), Match(17,she,she,()), Match(34,he,he,()), Match(34,her,her,()))

You can also use the += operator on the builder to add elements

builder += "it" -> ()

build()

When the build() method is invoked returns a finder and clears out all the data in the builder. It is possible to reuse the builder without interfering with already generated finders.

Matched results

Results are returned in a Match value that is defined as follows:

case class Match[T](start:Int,target:String,actual:String,data:T)

The start value is the offset in characters from the beginning of the input string to the first letter of the match. target is the string to match, actual was the actual string matched. It is possible that target and actual can differ (for example in case) because one of the optional arguments to the builder is a character map function that gets applied to each character in the dictionary (trie) and to each character during find. The default character map function maps everything to lower-case therefore case-insensitive matching is the default. Other interesting character map functions could include removing diacritical or accent marks from characters. data is arbitrary data associated with the dictionary entries that matched. You can supply the data when you add a word to the dictionary:

builder += "word" -> <data>

The data added must conform to a type, in the above example the type was Unit so () was supplied as the value.

License

This library is released under the Apache 2.0 license.