Method Sample

include/LightGBM/utils/random.h:69–98

! * \brief Sample K data from {0,1,...,N-1} * \param N * \param K * \return K Ordered sampled data from {0,1,...,N-1} */

  * \return K Ordered sampled data from {0,1,...,N-1}
  */
  inline std::vector<int> Sample(int N, int K) {
    std::vector<int> ret;
    ret.reserve(K);
    if (K > N || K <= 0) {
      return ret;
    } else if (K == N) {
      for (int i = 0; i < N; ++i) {
        ret.push_back(i);
      }
    } else if (K > 1 && K > (N / std::log2(K))) {
      for (int i = 0; i < N; ++i) {
        double prob = (K - ret.size()) / static_cast<double>(N - i);
        if (NextFloat() < prob) {
          ret.push_back(i);
        }
      }
    } else {
      std::set<int> sample_set;
      while (static_cast<int>(sample_set.size()) < K) {
        int next = RandInt32() % N;
        if (sample_set.count(next) == 0) {
          sample_set.insert(next);
        }
      }
      for (auto iter = sample_set.begin(); iter != sample_set.end(); ++iter) {
        ret.push_back(*iter);
      }
    }
    return ret;
  }

 private:
  inline int RandInt16() {