package cn.edu.bjut.chapter6;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Grouper<T> {
	private List<T> data;
	private int nfold; 
	private int[] starts = null;
	
	public Grouper(List<T> data, int nfold, long seed) {
		this.data = data; 
		this.nfold = nfold; 
		
		Collections.shuffle(data, new Random(seed));
		
		this.starts = new int[nfold + 1]; 
		for (int v = 0; v <= nfold; v++) {
			starts[v] = Math.round(data.size() * (v / (float) nfold)); 
		}
	}

	public List<T> getGroup(final int split) {
		if (split >= nfold || split < 0) {
			return null; 
		} 
		
		List<T> group = new ArrayList<T>(); 
		for (int m = starts[split]; m < starts[split + 1]; m++) {
			group.add(data.get(m)); 
		}
		
		return group; 
	}
}