Java Collection Random Element rndSubset(final Collection c, final double ratio)

Description

Returns a random subset of the specified collection, so that its size is a specified ratio of the original collection size.

License

Open Source License

Parameter

Parameter	Description
T	Type parameter.
c	Collection to pick from.
ratio	Requested ratio.

Return

List of randomly picked elements of the collection.

Declaration

public static <T> List<T> rndSubset(final Collection<T> c, final double ratio) 

Method Source Code

//package com.java2s;
/*//from  w ww.  j  a  va2  s  . c  o m
 *  Copyright (C) 2010 vektor
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

import java.util.ArrayList;
import java.util.Collection;

import java.util.List;
import java.util.Random;

public class Main {
    private static final Random RND = new Random();

    /**
     * Returns a random subset of the specified collection, so that its size is a
     * specified ratio of the original collection size.
     *
     * @param <T> Type parameter.
     * @param c Collection to pick from.
     * @param ratio Requested ratio.
     * @return List of randomly picked elements of the collection.
     */
    public static <T> List<T> rndSubset(final Collection<T> c, final double ratio) {
        return rndSubset(c, (int) Math.round(c.size() * ratio));
    }

    /**
     * Returns a random subset of the specified collection of requested size.
     *
     * @param <T> Type parameter.
     * @param c Collection to pick from.
     * @param count Requested size of the subset.
     * @return List of randomly picked elements of the collection.
     */
    public static <T> List<T> rndSubset(final Collection<T> c, final int count) {
        if (c == null) {
            throw new IllegalArgumentException("Expecting non-null parameter");
        }
        if (count < 0) {
            throw new IllegalArgumentException("Size of the subset cannot be negative: " + count);
        }
        if (count > c.size()) {
            throw new IllegalArgumentException("Subset cannot be bigger than the original set: " + count);
        }

        final List<T> ret = new ArrayList<T>(count);
        final List<T> tmp = new ArrayList<T>(c);

        for (int i = 0; i < count; i++) {
            final int toRemove = RND.nextInt(tmp.size());
            ret.add(tmp.get(toRemove));
            tmp.remove(toRemove);
        }

        return ret;
    }
}

Related

1. random(Collection coll)
2. random(Collection coll)
3. randomElement(Collection coll)
4. randomElement(Collection in)
5. randomIterable(Collection col)
6. sampleWithReplacement(Collection c, int n)
7. selectRandom(Collection set)
8. selectRandom(Collection col)
9. selectRandomSubset(Collection col, int count)