source: ip/src/main/java/geniusweb/ip/general/RandomSubsetOfGivenSet.java@ 39

package geniusweb.ip.general;

import java.util.Random;

public class RandomSubsetOfGivenSet {
        final private int[] givenSet;
        final private int numOfElementsInGivenSet;
        final private int sizeOfSubsetToBeSampled;
        final private boolean subsetEqualsGivenSet;
        private int[] availableIndicesToChooseFrom;
        private Random randomGenerator;

        // ******************************************************************************************************

        /**
         * The constructor:
         * 
         * @param givenSet:                The set from which subsets will be
         *                                 sampled
         * @param numOfElementsInGivenSet: the number of elements in the set from
         *                                 which subsets will be sampled
         * @param sizeOfSubsetToBeSampled: the size of every subset that will be
         *                                 sampled.
         */
        public RandomSubsetOfGivenSet(int[] givenSet, int numOfElementsInGivenSet,
                        int sizeOfSubsetToBeSampled) {
                this.givenSet = givenSet;
                this.numOfElementsInGivenSet = numOfElementsInGivenSet;
                this.sizeOfSubsetToBeSampled = sizeOfSubsetToBeSampled;
                this.randomGenerator = new Random();
                this.availableIndicesToChooseFrom = new int[numOfElementsInGivenSet];
                if (sizeOfSubsetToBeSampled == numOfElementsInGivenSet)
                        subsetEqualsGivenSet = true;
                else
                        subsetEqualsGivenSet = false;
        }

        // ******************************************************************************************************

        /**
         * Returns random subset of size: "sizeOfSubsetToBeSampled", taken from the
         * set: "givenSet"
         */
        public int[] getSubsetInByteFormat() {
                if (this.subsetEqualsGivenSet) {
                        int[] copyOfGivenSet = new int[numOfElementsInGivenSet];
                        for (int i = 0; i < numOfElementsInGivenSet; i++) {
                                copyOfGivenSet[i] = givenSet[i];
                        }
                        return copyOfGivenSet;
                } else {
                        // this.randomGenerator = new Random();
                        for (int i = numOfElementsInGivenSet - 1; i >= 0; i--) {
                                availableIndicesToChooseFrom[i] = i;
                        }
                        int[] subsetInByteFormat = new int[sizeOfSubsetToBeSampled];
                        int indexInSubset = 0;
                        for (int i = numOfElementsInGivenSet
                                        - 1; i >= numOfElementsInGivenSet
                                                        - sizeOfSubsetToBeSampled; i--) {
                                int j = this.randomGenerator.nextInt(i + 1);
                                subsetInByteFormat[indexInSubset] = givenSet[availableIndicesToChooseFrom[j]];
                                indexInSubset++;
                                availableIndicesToChooseFrom[j] = availableIndicesToChooseFrom[i];
                        }
                        return subsetInByteFormat;
                }
        }

        // ******************************************************************************************************

        /**
         * Returns random subset of size: "sizeOfSubsetToBeSampled", taken from the
         * set: "givenSet"
         */
        public int getSubsetInBitFormat() {
                if (this.subsetEqualsGivenSet) {
                        int copyOfGivenSet = 0;
                        for (int i = 0; i < numOfElementsInGivenSet; i++) {
                                // Add agent "givenSet[i]" to "copyOfGivenSet"
                                copyOfGivenSet += 1 << (givenSet[i] - 1);
                        }
                        return copyOfGivenSet;
                } else {
                        // this.randomGenerator = new Random();
                        for (int i = numOfElementsInGivenSet - 1; i >= 0; i--) {
                                availableIndicesToChooseFrom[i] = i;
                        }
                        int subsetInBitFormat = 0;
                        int indexInSubset = 0;
                        for (int i = numOfElementsInGivenSet
                                        - 1; i >= numOfElementsInGivenSet
                                                        - sizeOfSubsetToBeSampled; i--) {
                                int j = this.randomGenerator.nextInt(i + 1);
                                // Add agent "givenSet[ availableIndicesToChooseFrom[ j ] ]" to
                                // "subsetInBitFormat"
                                subsetInBitFormat += 1 << (givenSet[availableIndicesToChooseFrom[j]]
                                                - 1);
                                indexInSubset++;
                                availableIndicesToChooseFrom[j] = availableIndicesToChooseFrom[i];
                        }
                        return subsetInBitFormat;
                }
        }
}