eu.project.ttc.utils.CollectionUtils.java Source code

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/*******************************************************************************
 * Copyright 2015-2016 - CNRS (Centre National de Recherche Scientifique)
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 eu.project.ttc.utils;

import java.util.List;
import java.util.Set;

import com.google.common.collect.Sets;

public class CollectionUtils {

    /**
     * 
     * Transforms a list of sets into a set of element pairs,
     * which is the union of all cartesian products of
     * all pairs of sets.
     * 
     * Example: 
     * 
     * A = {a,b,c}
     * B = {d}
     * C = {e, f}
     * 
     * returns AxB U AxC U BxC = {
     *    {a,d}, {b,d}, {c,d}, 
     *  {a,e}, {a,f}, {b,e}, {b,f}, {c,e}, {c,f},
     *  {d,e}, {d,f}
     * }
     * 
     * 
     * @param iterable
     * @return
     */
    @SuppressWarnings("unchecked")
    public static <T extends Comparable<? super T>> Set<Pair<T>> combineAndProduct(
            List<? extends Set<? extends T>> sets) {
        Set<Pair<T>> results = Sets.newHashSet();
        for (int i = 0; i < sets.size(); i++) {
            for (int j = i + 1; j < sets.size(); j++)
                for (List<T> l : Sets.cartesianProduct(sets.get(i), sets.get(j)))
                    results.add(new Pair<T>(l.get(0), l.get(1)));
        }
        return results;
    }

}