Generate random number with non-uniform density

Question

Did someone know how to generate random numbers with a non-uniform density?

Answer 1

This class takes a distribution as a matrix (each row is a couple of a number and its frequency) and generates random numbers. So you can have Look at main method and run.

public class RandomGenerator {
    HashMap mappa = new HashMap();
    Random random = new Random();
    int max;




    public static void main(String as[]){ 
        int[][] matrice = new int[3][2];
        //number 5 occurs 5 times
        matrice[0][0] = 5 ;
        matrice[0][1] = 5 ;
        //number 18 occurs 18 times
        matrice[1][0] = 18 ;
        matrice[1][1] = 18 ;
        //number 77 occurs 77 times
        matrice[2][0] = 77 ;
        matrice[2][1] = 77 ;

        RandomGenerator randomGenerator = new RandomGenerator(matrice); 


        for (int i = 0; i < 100; i++) {
            System.out.println( randomGenerator.getNext() );
        }
    }





    public int getNext(){
        int percentile = random.nextInt(max);
        Range r =mappa.get(percentile);
        return r.getValMax();
    }

    public HashMap getMappa() {
        return mappa;
    }

    public void setMappa(HashMap mappa) {
        this.mappa = mappa;
    }

    public RandomGenerator(int[][] distribuzioneOriginale ){
        ArrayList listaRange = new ArrayList();
        int previous = 0;
        int totaleOccorrenze = 0;
        for (int riga = 0; riga < distribuzioneOriginale.length; riga++) {

            Range r = new Range();
            r.setValMin(previous);
            r.setValMax(distribuzioneOriginale[riga][0]);
            r.setOccorrenze(distribuzioneOriginale[riga][1]);
            totaleOccorrenze += distribuzioneOriginale[riga][1];
            previous = distribuzioneOriginale[riga][0];

            listaRange.add(r);
        }



        int indice = 0;
        for (int iRange = 0; iRange < listaRange.size(); iRange++) {
            Range r = listaRange.get(iRange);

            int perc = (int) ( 1000* (r.getOccorrenze() / (double)  totaleOccorrenze)  )  ;

            for (int i = 0; i < perc; i++) {
                mappa.put( i + indice  , r);
            }
            indice += perc;
        }

        max = indice;

    }



    class Range{
        int valMin;
        int valMax;
        int occorrenze; 


        public int getValMin() {
            return valMin;
        }
        public void setValMin(int valMin) {
            this.valMin = valMin;
        }
        public int getValMax() {
            return valMax;
        }
        public void setValMax(int valMax) {
            this.valMax = valMax;
        }
        public int getOccorrenze() {
            return occorrenze;
        }
        public void setOccorrenze(int occorrenze) {
            this.occorrenze = occorrenze;
        }  

    }
}