bin.cpp

#include <LightGBM/utils/common.h>
#include <LightGBM/bin.h>

#include "dense_bin.hpp"
#include "dense_nbits_bin.hpp"
#include "sparse_bin.hpp"
#include "ordered_sparse_bin.hpp"

#include <cmath>
#include <cstring>
#include <cstdint>

#include <limits>
#include <vector>
#include <algorithm>

namespace LightGBM {

BinMapper::BinMapper() {
}

// deep copy function for BinMapper
BinMapper::BinMapper(const BinMapper& other) {
  num_bin_ = other.num_bin_;
  is_trival_ = other.is_trival_;
  sparse_rate_ = other.sparse_rate_;
  bin_upper_bound_ = other.bin_upper_bound_;
  min_val_ = other.min_val_;
  max_val_ = other.max_val_;
  default_bin_ = other.default_bin_;
}

BinMapper::BinMapper(const void* memory) {
  CopyFrom(reinterpret_cast<const char*>(memory));
}

BinMapper::~BinMapper() {

}

bool NeedFilter(std::vector<int>& cnt_in_bin, int total_cnt, int filter_cnt) {
  int sum_left = 0;
  for (size_t i = 0; i < cnt_in_bin.size() - 1; ++i) {
    sum_left += cnt_in_bin[i];
    if (sum_left >= filter_cnt) {
      return false;
    } else if (total_cnt - sum_left >= filter_cnt) {
      return false;
    }
  }
  return true;
}

void BinMapper::FindBin(std::vector<double>& values, size_t total_sample_cnt,
  int max_bin, int min_data_in_bin, int min_split_data) {
  // limit max_bin by min_data_in_bin
  std::vector<double>& raw_values = values;
  int zero_cnt = static_cast<int>(total_sample_cnt - raw_values.size());
  // find distinct_values first
  std::vector<double> distinct_values;
  std::vector<int> counts;

  std::sort(raw_values.begin(), raw_values.end());

  // push zero in the front
  if (raw_values.empty() || (raw_values[0] > 0.0f && zero_cnt > 0)) {
    distinct_values.push_back(0.0f);
    counts.push_back(zero_cnt);
  }

  if (!raw_values.empty()) {
    distinct_values.push_back(raw_values[0]);
    counts.push_back(1);
  }

  for (size_t i = 1; i < raw_values.size(); ++i) {
    if (raw_values[i] != raw_values[i - 1]) {
      if (raw_values[i - 1] < 0.0f && raw_values[i] > 0.0f) {
        distinct_values.push_back(0.0f);
        counts.push_back(zero_cnt);
      }
      distinct_values.push_back(raw_values[i]);
      counts.push_back(1);
    } else {
      ++counts.back();
    }
  }

  // push zero in the back
  if (!raw_values.empty() && raw_values.back() < 0.0f && zero_cnt > 0) {
    distinct_values.push_back(0.0f);
    counts.push_back(zero_cnt);
  }
  min_val_ = distinct_values.front();
  max_val_ = distinct_values.back();
  std::vector<int> cnt_in_bin;
  int num_values = static_cast<int>(distinct_values.size());

  if (num_values <= max_bin) {
    // use distinct value is enough
    bin_upper_bound_.clear();
    int cur_cnt_inbin = 0;
    for (int i = 0; i < num_values - 1; ++i) {
      cur_cnt_inbin += counts[i];
      if (cur_cnt_inbin >= min_data_in_bin) {
        bin_upper_bound_.push_back((distinct_values[i] + distinct_values[i + 1]) / 2);
        cnt_in_bin.push_back(cur_cnt_inbin);
        cur_cnt_inbin = 0;
      }
    }
    cur_cnt_inbin += counts.back();
    cnt_in_bin.push_back(cur_cnt_inbin);
    bin_upper_bound_.push_back(std::numeric_limits<double>::infinity());
    num_bin_ = static_cast<int>(bin_upper_bound_.size());
  } else {
    if (min_data_in_bin > 0) {
      max_bin = std::min(max_bin, static_cast<int>(total_sample_cnt / min_data_in_bin));
      max_bin = std::max(max_bin, 1);
    }
    double mean_bin_size = static_cast<double>(total_sample_cnt) / max_bin;
    if (zero_cnt > mean_bin_size) {
      int non_zero_cnt = static_cast<int>(raw_values.size());
      max_bin = std::min(max_bin, 1 + static_cast<int>(non_zero_cnt / min_data_in_bin));
    }
    // mean size for one bin
    int rest_bin_cnt = max_bin;
    int rest_sample_cnt = static_cast<int>(total_sample_cnt);
    std::vector<bool> is_big_count_value(num_values, false);
    for (int i = 0; i < num_values; ++i) {
      if (counts[i] >= mean_bin_size) {
        is_big_count_value[i] = true;
        --rest_bin_cnt;
        rest_sample_cnt -= counts[i];
      }
    }
    mean_bin_size = static_cast<double>(rest_sample_cnt) / rest_bin_cnt;
    std::vector<double> upper_bounds(max_bin, std::numeric_limits<double>::infinity());
    std::vector<double> lower_bounds(max_bin, std::numeric_limits<double>::infinity());

    int bin_cnt = 0;
    lower_bounds[bin_cnt] = distinct_values[0];
    int cur_cnt_inbin = 0;
    for (int i = 0; i < num_values - 1; ++i) {
      if (!is_big_count_value[i]) {
        rest_sample_cnt -= counts[i];
      }
      cur_cnt_inbin += counts[i];
      // need a new bin
      if (is_big_count_value[i] || cur_cnt_inbin >= mean_bin_size ||
        (is_big_count_value[i + 1] && cur_cnt_inbin >= std::max(1.0, mean_bin_size * 0.5f))) {
        upper_bounds[bin_cnt] = distinct_values[i];
        cnt_in_bin.push_back(cur_cnt_inbin);
        ++bin_cnt;
        lower_bounds[bin_cnt] = distinct_values[i + 1];
        if (bin_cnt >= max_bin - 1) { break; }
        cur_cnt_inbin = 0;
        if (!is_big_count_value[i]) {
          --rest_bin_cnt;
          mean_bin_size = rest_sample_cnt / static_cast<double>(rest_bin_cnt);
        }
      }
    }
    cur_cnt_inbin += counts.back();
    cnt_in_bin.push_back(cur_cnt_inbin);
    ++bin_cnt;
    // update bin upper bound
    bin_upper_bound_ = std::vector<double>(bin_cnt);
    num_bin_ = bin_cnt;
    for (int i = 0; i < bin_cnt - 1; ++i) {
      bin_upper_bound_[i] = (upper_bounds[i] + lower_bounds[i + 1]) / 2.0f;
    }
    // last bin upper bound
    bin_upper_bound_[bin_cnt - 1] = std::numeric_limits<double>::infinity();
  }

  // check trival(num_bin_ == 1) feature
  if (num_bin_ <= 1) {
    is_trival_ = true;
    default_bin_ = 0;
  } else {
    is_trival_ = false;
    default_bin_ = ValueToBin(0);
  }
  if (NeedFilter(cnt_in_bin, static_cast<int>(total_sample_cnt), min_split_data)) {
    is_trival_ = true;
  }
  // calculate sparse rate
  CHECK(num_bin_ <= max_bin);
  sparse_rate_ = static_cast<double>(cnt_in_bin[GetDefaultBin()]) / static_cast<double>(total_sample_cnt);
}


int BinMapper::SizeForSpecificBin(int bin) {
  int size = 0;
  size += sizeof(int);
  size += sizeof(bool);
  size += sizeof(double);
  size += 2 * sizeof(double);
  size += bin * sizeof(double);
  size += sizeof(uint32_t);
  return size;
}

void BinMapper::CopyTo(char * buffer) {
  std::memcpy(buffer, &num_bin_, sizeof(num_bin_));
  buffer += sizeof(num_bin_);
  std::memcpy(buffer, &is_trival_, sizeof(is_trival_));
  buffer += sizeof(is_trival_);
  std::memcpy(buffer, &sparse_rate_, sizeof(sparse_rate_));
  buffer += sizeof(sparse_rate_);
  std::memcpy(&min_val_, buffer, sizeof(min_val_));
  buffer += sizeof(min_val_);
  std::memcpy(&max_val_, buffer, sizeof(max_val_));
  buffer += sizeof(max_val_);
  std::memcpy(&default_bin_, buffer, sizeof(default_bin_));
  buffer += sizeof(default_bin_);
  std::memcpy(buffer, bin_upper_bound_.data(), num_bin_ * sizeof(double));
}

void BinMapper::CopyFrom(const char * buffer) {
  std::memcpy(&num_bin_, buffer, sizeof(num_bin_));
  buffer += sizeof(num_bin_);
  std::memcpy(&is_trival_, buffer, sizeof(is_trival_));
  buffer += sizeof(is_trival_);
  std::memcpy(&sparse_rate_, buffer, sizeof(sparse_rate_));
  buffer += sizeof(sparse_rate_);
  std::memcpy(&min_val_, buffer, sizeof(min_val_));
  buffer += sizeof(min_val_);
  std::memcpy(&max_val_, buffer, sizeof(max_val_));
  buffer += sizeof(max_val_);
  std::memcpy(&default_bin_, buffer, sizeof(default_bin_));
  buffer += sizeof(default_bin_);
  bin_upper_bound_ = std::vector<double>(num_bin_);
  std::memcpy(bin_upper_bound_.data(), buffer, num_bin_ * sizeof(double));
}

void BinMapper::SaveBinaryToFile(FILE* file) const {
  fwrite(&num_bin_, sizeof(num_bin_), 1, file);
  fwrite(&is_trival_, sizeof(is_trival_), 1, file);
  fwrite(&sparse_rate_, sizeof(sparse_rate_), 1, file);
  fwrite(&min_val_, sizeof(min_val_), 1, file);
  fwrite(&max_val_, sizeof(max_val_), 1, file);
  fwrite(&default_bin_, sizeof(default_bin_), 1, file);
  fwrite(bin_upper_bound_.data(), sizeof(double), num_bin_, file);
}

size_t BinMapper::SizesInByte() const {
  size_t ret = sizeof(num_bin_) + sizeof(is_trival_) + sizeof(sparse_rate_)
    + sizeof(min_val_) + sizeof(max_val_) + sizeof(default_bin_);
  ret += sizeof(double) *  num_bin_;
  return ret;
}

template class DenseBin<uint8_t>;
template class DenseBin<uint16_t>;
template class DenseBin<uint32_t>;

template class SparseBin<uint8_t>;
template class SparseBin<uint16_t>;
template class SparseBin<uint32_t>;

template class OrderedSparseBin<uint8_t>;
template class OrderedSparseBin<uint16_t>;
template class OrderedSparseBin<uint32_t>;

double BinMapper::kSparseThreshold = 0.8f;

Bin* Bin::CreateBin(data_size_t num_data, int num_bin, double sparse_rate, 
  bool is_enable_sparse, bool* is_sparse) {
  // sparse threshold
  if (sparse_rate >= BinMapper::kSparseThreshold && is_enable_sparse) {
    *is_sparse = true;
    return CreateSparseBin(num_data, num_bin);
  } else {
    *is_sparse = false;
    return CreateDenseBin(num_data, num_bin);
  }
}

Bin* Bin::CreateDenseBin(data_size_t num_data, int num_bin) {
  if (num_bin <= 16) {
    return new Dense4bitsBin(num_data);
  } else if (num_bin <= 256) {
    return new DenseBin<uint8_t>(num_data);
  } else if (num_bin <= 65536) {
    return new DenseBin<uint16_t>(num_data);
  } else {
    return new DenseBin<uint32_t>(num_data);
  }
}

Bin* Bin::CreateSparseBin(data_size_t num_data, int num_bin) {
  if (num_bin <= 256) {
    return new SparseBin<uint8_t>(num_data);
  } else if (num_bin <= 65536) {
    return new SparseBin<uint16_t>(num_data);
  } else {
    return new SparseBin<uint32_t>(num_data);
  }
}

}  // namespace LightGBM