Function SampleNoReplace

inst/include/Rcpp/sugar/functions/sample.h:255–291

Adapted from `ProbSampleNoReplace` Index version

// Adapted from `ProbSampleNoReplace`
// Index version
inline Vector<INTSXP> SampleNoReplace(Vector<REALSXP>& p, int n, int nans, bool one_based)
{
    Vector<INTSXP> perm = no_init(n), ans = no_init(nans);
    double rT, mass, totalmass;
    int i, j, k, n1;

    int adj = one_based ? 0 : 1;

    for (i = 0; i < n; i++) {
        perm[i] = i + 1;
    }

    Rf_revsort(p.begin(), perm.begin(), n);

    totalmass = 1.0;
    for (i = 0, n1 = n - 1; i < nans; i++, n1--) {
        rT = totalmass * unif_rand();
        mass = 0.0;

        for (j = 0; j < n1; j++) {
            mass += p[j];
            if (rT <= mass) {
                break;
            }
        }

        ans[i] = perm[j] - adj;
        totalmass -= p[j];

        for (k = j; k < n1; k++) {
            p[k] = p[k + 1];
            perm[k] = perm[k + 1];
        }
    }

    return ans;
}

// Element version
template <int RTYPE>