cc.recommenders.collections.SublistSelector.java Source code

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Here is the source code for cc.recommenders.collections.SublistSelector.java

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/**
 * Copyright (c) 2011-2013 Darmstadt University of Technology.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     Sebastian Proksch - initial API and implementation
 */
package cc.recommenders.collections;

import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

public class SublistSelector {

    public static <T> List<T> pickRandomSublist(List<T> in, int numToPick) {

        List<T> sublist = shuffle(in);

        if (sublist.size() > numToPick) {

            Iterator<T> iterator = sublist.iterator();
            skip(numToPick, iterator);
            removeAllRemaining(iterator);
        }

        return sublist;
    }

    public static <T> List<T> shuffle(List<T> in) {
        LinkedList<T> sublist = Lists.<T>newLinkedList();
        copyTo(in, sublist);
        Collections.shuffle(sublist);
        return sublist;
    }

    public static <T> Set<T> shuffle(Set<T> in) {
        List<T> sublist = Lists.<T>newLinkedList();
        copyTo(in, sublist);
        Collections.shuffle(sublist);
        Set<T> subset = Sets.newLinkedHashSet(sublist);
        return subset;
    }

    public static <T> List<T> forceShuffle(List<T> in) {
        LinkedList<T> sublist = Lists.<T>newLinkedList();
        copyTo(in, sublist);
        if (sublist.size() > 1) {
            while (sublist.equals(in)) {
                Collections.shuffle(sublist);
            }
        }
        return sublist;
    }

    private static void skip(int numToPick, Iterator<?> iterator) {
        int i = 0;
        while (i < numToPick) {
            iterator.next();
            i++;
        }
    }

    private static void removeAllRemaining(Iterator<?> iterator) {
        while (iterator.hasNext()) {
            iterator.next();
            iterator.remove();
        }
    }

    private static <T> void copyTo(Iterable<T> in, Collection<T> to) {
        for (T elem : in) {
            to.add(elem);
        }
    }
}