Method CopySubset

src/io/sparse_bin.hpp:377–412

  }

  void CopySubset(const Bin* full_bin, const data_size_t* used_indices, data_size_t num_used_indices) override {
    auto other_bin = dynamic_cast<const SparseBin<VAL_T>*>(full_bin);
    deltas_.clear();
    vals_.clear();
    data_size_t start = 0;
    if (num_used_indices > 0) {
      start = used_indices[0];
    }
    SparseBinIterator<VAL_T> iterator(other_bin, start);
    // transform to delta array
    data_size_t last_idx = 0;
    for (data_size_t i = 0; i < num_used_indices; ++i) {
      VAL_T bin = iterator.InnerRawGet(used_indices[i]);
      if (bin > 0) {
        data_size_t cur_delta = i - last_idx;
        while (cur_delta >= 256) {
          deltas_.push_back(cur_delta & 0xff);
          vals_.push_back(0);
          cur_delta >>= 8;
        }
        deltas_.push_back(static_cast<uint8_t>(cur_delta));
        vals_.push_back(bin);
        last_idx = i;
      }
    }
    // avoid out of range
    deltas_.push_back(0);
    num_vals_ = static_cast<data_size_t>(vals_.size());

    // reduce memory cost
    deltas_.shrink_to_fit();
    vals_.shrink_to_fit();

    // generate fast index
    GetFastIndex();
  }

  SparseBin<VAL_T>* Clone() override;