PIteration.java

/***********************************************************************************************************************
 *
 * Copyright (C) 2010-2014 by the Stratosphere project (http://stratosphere.eu)
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 *
 **********************************************************************************************************************/

package hu.sztaki.stratosphere.workshop.batch.als;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import Jama.Matrix;

import eu.stratosphere.util.Collector;
import eu.stratosphere.api.java.functions.CoGroupFunction;
import eu.stratosphere.api.java.tuple.Tuple2;
import eu.stratosphere.api.java.tuple.Tuple3;

public class PIteration extends CoGroupFunction<Tuple3<Integer,Integer,Double>,Tuple3<Integer,Integer,double[]>,Tuple2<Integer,double[]>> {

	private int k;
	private double lambda;
	private int id_;
	private Tuple2<Integer,double[]> result_ = new Tuple2();

	public PIteration(int k, double lambda) {
		this.k = k;
		this.lambda = lambda;
	}

	@Override
	public void coGroup(Iterator<Tuple3<Integer,Integer,Double>> matrixElements, Iterator<Tuple3<Integer,Integer,double[]>> q,
						Collector<Tuple2<Integer,double[]>> out) {
		double[][] matrix = new double[k][k];
		double[][] vector = new double[k][1];

		//Don't do anything if q is empty
		if(!q.hasNext()){
			return;
		}

		double element_ = lambda; //Regularization with Frobenius-norm

		if(lambda != 0.0) {
			for(double[] row : matrix) {
				Arrays.fill(row, element_);
			}
		}

		Map<Integer, Double> ratings = new HashMap<Integer, Double>();
		while (matrixElements.hasNext()) {

			//TODO: Fill the ratings map with (columnId,elementValue) pairs from matrixElements



		}

		while (q.hasNext()) {
			Tuple3<Integer,Integer,double[]> column = q.next();
			double[] column_elements = column.f2;
			id_ = column.f0;
			double rating = ratings.get(column.f1);
			for (int i = 0; i < k; ++i) {
				for (int j = 0; j < k; ++j) {
					matrix[i][j] += column_elements[i] * column_elements[j];
				}
				vector[i][0] += rating * column_elements[i];
			}
		}

		Matrix a = new Matrix(matrix);
		Matrix b = new Matrix(vector);
		Matrix result = a.solve(b);

		double[] result_elements = new double[k];
		for (int i = 0; i < k; ++i) {
			result_elements[i] = result.get(i, 0);
		}
		result_.setFields(id_, result_elements);
		out.collect(result_);
	}

}