FP lifetime: subtracting iterators

[pfultz2]

int count_distinct(double *data, int len) {
    if( len == 0)
        return 0;
    std::vector<double> v;
    v.assign(data, data + len);
    std::sort(v.begin(), v.end());
    return std::unique(v.begin(), v.end()) - v.begin();
}