PhraseSimilarity.java

package ruc.irm.similarity.phrase;

import java.util.ArrayList;
import java.util.List;

import ruc.irm.similarity.Similaritable;

/**
 * 一种简单的短语相似度计算方法，算法原理请参考《中文信息相似度计算理论与方法》一书P69.
 * 
 * @author <a href="mailto:iamxiatian@gmail.com">夏天</a>
 * @organization 中国人民大学信息资源管理学院 知识工程实验室
 */
public class PhraseSimilarity implements Similaritable {

	@Override
	public double getSimilarity(String item1, String item2) {
		return (getSC(item1, item2) + getSC(item2, item1)) / 2.0;
	}

	public List<Integer> getC(String first, String second, int pos) {
		List<Integer> results = new ArrayList<Integer>();
		char ch = first.charAt(pos);
		for (int i = 0; i < second.length(); i++) {
			if (ch == second.charAt(i)) {
				results.add(i);
			}
		}
		return results;
	}

	public int getDistance(String first, String second, int pos) {
		int d = second.length();
		for (int k : getC(first, second, pos)) {
			int value = Math.abs(k - pos);
			if (d > value) {
				d = value;
			}
		}

		return d;
	}

	public double getCC(String first, String second, int pos) {
		return (second.length() - getDistance(first, second, pos)) * 1.0 / second.length();
	}

	public double getSC(String first, String second) {
		double total = 0.0;
		for (int i = 0; i < first.length(); i++) {
			total = total + getCC(first, second, i);
		}
		return total / first.length();
	}

}