Java – NaN Quantitavity – Quant Trading, Statistical Learning, Coding and Brainstorming

Random Permutation 2 – Random sample m out of n

weekendsunny — Thu, 14 Mar 2013 02:31:18 +0000

int[] pickMRandomly(int[] array, int m) {
    int[] subset = new int[m];
    for (int j = 0; j < m; j++) {
        int index = random(j, n); // random number between j and n
        int temp = array[index];
        array[index] = array[j];
        array[j] = temp;
        subset[j] = temp;
    }
    return subset;
}

Random Permutation 1 – shuffle

weekendsunny — Thu, 14 Mar 2013 02:29:21 +0000

public static void shuffleArray(int[] array) {
    Random generator = new Random();
    for (int j = 0; j < array.length; j++) {
    int index = generator.nextInt(array.length-j)+j; // random number between j and n
    int temp = array[index];
    array[index] = array[j];
    array[j] = temp;
    }
}