info.debatty.java.stringsimilarity

Class ShingleBased

java.lang.Object

info.debatty.java.stringsimilarity.ShingleBased

Direct Known Subclasses:

Cosine, Jaccard, QGram, SorensenDice

@Immutable
public abstract class ShingleBased
extends Object

Abstract class for string similarities that rely on set operations (like cosine similarity or jaccard index). k-shingling is the operation of transforming a string (or text document) into a set of n-grams, which can be used to measure the similarity between two strings or documents. Generally speaking, a k-gram is any sequence of k tokens. We use here the definition from Leskovec, Rajaraman & Ullman (2014), "Mining of Massive Datasets", Cambridge University Press: Multiple subsequent spaces are replaced by a single space, and a k-gram is a sequence of k characters. Default value of k is 3. A good rule of thumb is to imagine that there are only 20 characters and estimate the number of k-shingles as 20^k. For small documents like e-mails, k = 5 is a recommended value. For large documents, such as research articles, k = 9 is considered a safe choice.

Author:

Thibault Debatty

Constructor Summary

Constructors

Constructor and Description
ShingleBased(int k)

Method Summary

Modifier and Type	Method and Description
int	getK() Return k, the length of k-shingles (aka n-grams).
Map<String,Integer>	getProfile(String string) Compute and return the profile of s, as defined by Ukkonen "Approximate string-matching with q-grams and maximal matches".

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ShingleBased

public ShingleBased(int k)

Parameters:

k -

Throws:

IllegalArgumentException - if k is <= 0

Method Detail

getK

public final int getK()

Return k, the length of k-shingles (aka n-grams).

Returns:

The length of k-shingles.

getProfile

public final Map<String,Integer> getProfile(String string)

Compute and return the profile of s, as defined by Ukkonen "Approximate string-matching with q-grams and maximal matches". https://www.cs.helsinki.fi/u/ukkonen/TCS92.pdf The profile is the number of occurrences of k-shingles, and is used to compute q-gram similarity, Jaccard index, etc. Pay attention: the memory requirement of the profile can be up to k * size of the string

Parameters:

string -

Returns:

the profile of this string, as an unmodifiable Map