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xgboost/src/tree/updater_basemaker-inl.h

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/*!
* Copyright 2014 by Contributors
* \file updater_basemaker-inl.h
* \brief implement a common tree constructor
* \author Tianqi Chen
*/
#ifndef XGBOOST_TREE_UPDATER_BASEMAKER_INL_H_
#define XGBOOST_TREE_UPDATER_BASEMAKER_INL_H_
#include <xgboost/base.h>
#include <xgboost/tree_updater.h>
#include <vector>
#include <algorithm>
#include <string>
#include <limits>
#include <utility>
#include "./param.h"
#include "../common/sync.h"
#include "../common/io.h"
#include "../common/random.h"
#include "../common/quantile.h"
namespace xgboost {
namespace tree {
/*!
* \brief base tree maker class that defines common operation
* needed in tree making
*/
class BaseMaker: public TreeUpdater {
public:
void Init(const std::vector<std::pair<std::string, std::string> >& args) override {
param.InitAllowUnknown(args);
}
protected:
// helper to collect and query feature meta information
struct FMetaHelper {
public:
/*! \brief find type of each feature, use column format */
inline void InitByCol(DMatrix* p_fmat,
const RegTree& tree) {
fminmax.resize(tree.param.num_feature * 2);
std::fill(fminmax.begin(), fminmax.end(),
-std::numeric_limits<bst_float>::max());
// start accumulating statistics
dmlc::DataIter<ColBatch>* iter = p_fmat->ColIterator();
iter->BeforeFirst();
while (iter->Next()) {
const ColBatch& batch = iter->Value();
for (bst_uint i = 0; i < batch.size; ++i) {
const bst_uint fid = batch.col_index[i];
const ColBatch::Inst& c = batch[i];
if (c.length != 0) {
fminmax[fid * 2 + 0] = std::max(-c[0].fvalue, fminmax[fid * 2 + 0]);
fminmax[fid * 2 + 1] = std::max(c[c.length - 1].fvalue, fminmax[fid * 2 + 1]);
}
}
}
rabit::Allreduce<rabit::op::Max>(dmlc::BeginPtr(fminmax), fminmax.size());
}
// get feature type, 0:empty 1:binary 2:real
inline int Type(bst_uint fid) const {
CHECK_LT(fid * 2 + 1, fminmax.size())
<< "FeatHelper fid exceed query bound ";
bst_float a = fminmax[fid * 2];
bst_float b = fminmax[fid * 2 + 1];
if (a == -std::numeric_limits<bst_float>::max()) return 0;
if (-a == b) {
return 1;
} else {
return 2;
}
}
inline bst_float MaxValue(bst_uint fid) const {
return fminmax[fid *2 + 1];
}
inline void SampleCol(float p, std::vector<bst_uint> *p_findex) const {
std::vector<bst_uint> &findex = *p_findex;
findex.clear();
for (size_t i = 0; i < fminmax.size(); i += 2) {
const bst_uint fid = static_cast<bst_uint>(i / 2);
if (this->Type(fid) != 0) findex.push_back(fid);
}
unsigned n = static_cast<unsigned>(p * findex.size());
std::shuffle(findex.begin(), findex.end(), common::GlobalRandom());
findex.resize(n);
// sync the findex if it is subsample
std::string s_cache;
common::MemoryBufferStream fc(&s_cache);
dmlc::Stream& fs = fc;
if (rabit::GetRank() == 0) {
fs.Write(findex);
}
rabit::Broadcast(&s_cache, 0);
fs.Read(&findex);
}
private:
std::vector<bst_float> fminmax;
};
// ------static helper functions ------
// helper function to get to next level of the tree
/*! \brief this is helper function for row based data*/
inline static int NextLevel(const RowBatch::Inst &inst, const RegTree &tree, int nid) {
const RegTree::Node &n = tree[nid];
bst_uint findex = n.split_index();
for (unsigned i = 0; i < inst.length; ++i) {
if (findex == inst[i].index) {
if (inst[i].fvalue < n.split_cond()) {
return n.cleft();
} else {
return n.cright();
}
}
}
return n.cdefault();
}
/*! \brief get number of omp thread in current context */
inline static int get_nthread() {
int nthread;
#pragma omp parallel
{
nthread = omp_get_num_threads();
}
return nthread;
}
// ------class member helpers---------
/*! \brief initialize temp data structure */
inline void InitData(const std::vector<bst_gpair> &gpair,
const DMatrix &fmat,
const RegTree &tree) {
CHECK_EQ(tree.param.num_nodes, tree.param.num_roots)
<< "TreeMaker: can only grow new tree";
const std::vector<unsigned> &root_index = fmat.info().root_index;
{
// setup position
position.resize(gpair.size());
if (root_index.size() == 0) {
std::fill(position.begin(), position.end(), 0);
} else {
for (size_t i = 0; i < position.size(); ++i) {
position[i] = root_index[i];
CHECK_LT(root_index[i], (unsigned)tree.param.num_roots)
<< "root index exceed setting";
}
}
// mark delete for the deleted datas
for (size_t i = 0; i < position.size(); ++i) {
if (gpair[i].hess < 0.0f) position[i] = ~position[i];
}
// mark subsample
if (param.subsample < 1.0f) {
std::bernoulli_distribution coin_flip(param.subsample);
auto& rnd = common::GlobalRandom();
for (size_t i = 0; i < position.size(); ++i) {
if (gpair[i].hess < 0.0f) continue;
if (!coin_flip(rnd)) position[i] = ~position[i];
}
}
}
{
// expand query
qexpand.reserve(256); qexpand.clear();
for (int i = 0; i < tree.param.num_roots; ++i) {
qexpand.push_back(i);
}
this->UpdateNode2WorkIndex(tree);
}
}
/*! \brief update queue expand add in new leaves */
inline void UpdateQueueExpand(const RegTree &tree) {
std::vector<int> newnodes;
for (size_t i = 0; i < qexpand.size(); ++i) {
const int nid = qexpand[i];
if (!tree[nid].is_leaf()) {
newnodes.push_back(tree[nid].cleft());
newnodes.push_back(tree[nid].cright());
}
}
// use new nodes for qexpand
qexpand = newnodes;
this->UpdateNode2WorkIndex(tree);
}
// return decoded position
inline int DecodePosition(bst_uint ridx) const {
const int pid = position[ridx];
return pid < 0 ? ~pid : pid;
}
// encode the encoded position value for ridx
inline void SetEncodePosition(bst_uint ridx, int nid) {
if (position[ridx] < 0) {
position[ridx] = ~nid;
} else {
position[ridx] = nid;
}
}
/*!
* \brief this is helper function uses column based data structure,
* reset the positions to the lastest one
* \param nodes the set of nodes that contains the split to be used
* \param p_fmat feature matrix needed for tree construction
* \param tree the regression tree structure
*/
inline void ResetPositionCol(const std::vector<int> &nodes,
DMatrix *p_fmat,
const RegTree &tree) {
// set the positions in the nondefault
this->SetNonDefaultPositionCol(nodes, p_fmat, tree);
// set rest of instances to default position
const std::vector<bst_uint> &rowset = p_fmat->buffered_rowset();
// set default direct nodes to default
// for leaf nodes that are not fresh, mark then to ~nid,
// so that they are ignored in future statistics collection
const bst_omp_uint ndata = static_cast<bst_omp_uint>(rowset.size());
#pragma omp parallel for schedule(static)
for (bst_omp_uint i = 0; i < ndata; ++i) {
const bst_uint ridx = rowset[i];
const int nid = this->DecodePosition(ridx);
if (tree[nid].is_leaf()) {
// mark finish when it is not a fresh leaf
if (tree[nid].cright() == -1) {
position[ridx] = ~nid;
}
} else {
// push to default branch
if (tree[nid].default_left()) {
this->SetEncodePosition(ridx, tree[nid].cleft());
} else {
this->SetEncodePosition(ridx, tree[nid].cright());
}
}
}
}
/*!
* \brief this is helper function uses column based data structure,
* update all positions into nondefault branch, if any, ignore the default branch
* \param nodes the set of nodes that contains the split to be used
* \param p_fmat feature matrix needed for tree construction
* \param tree the regression tree structure
*/
virtual void SetNonDefaultPositionCol(const std::vector<int> &nodes,
DMatrix *p_fmat,
const RegTree &tree) {
// step 1, classify the non-default data into right places
std::vector<unsigned> fsplits;
for (size_t i = 0; i < nodes.size(); ++i) {
const int nid = nodes[i];
if (!tree[nid].is_leaf()) {
fsplits.push_back(tree[nid].split_index());
}
}
std::sort(fsplits.begin(), fsplits.end());
fsplits.resize(std::unique(fsplits.begin(), fsplits.end()) - fsplits.begin());
dmlc::DataIter<ColBatch> *iter = p_fmat->ColIterator(fsplits);
while (iter->Next()) {
const ColBatch &batch = iter->Value();
for (size_t i = 0; i < batch.size; ++i) {
ColBatch::Inst col = batch[i];
const bst_uint fid = batch.col_index[i];
const bst_omp_uint ndata = static_cast<bst_omp_uint>(col.length);
#pragma omp parallel for schedule(static)
for (bst_omp_uint j = 0; j < ndata; ++j) {
const bst_uint ridx = col[j].index;
const float fvalue = col[j].fvalue;
const int nid = this->DecodePosition(ridx);
// go back to parent, correct those who are not default
if (!tree[nid].is_leaf() && tree[nid].split_index() == fid) {
if (fvalue < tree[nid].split_cond()) {
this->SetEncodePosition(ridx, tree[nid].cleft());
} else {
this->SetEncodePosition(ridx, tree[nid].cright());
}
}
}
}
}
}
/*! \brief helper function to get statistics from a tree */
template<typename TStats>
inline void GetNodeStats(const std::vector<bst_gpair> &gpair,
const DMatrix &fmat,
const RegTree &tree,
std::vector< std::vector<TStats> > *p_thread_temp,
std::vector<TStats> *p_node_stats) {
std::vector< std::vector<TStats> > &thread_temp = *p_thread_temp;
const MetaInfo &info = fmat.info();
thread_temp.resize(this->get_nthread());
p_node_stats->resize(tree.param.num_nodes);
#pragma omp parallel
{
const int tid = omp_get_thread_num();
thread_temp[tid].resize(tree.param.num_nodes, TStats(param));
for (size_t i = 0; i < qexpand.size(); ++i) {
const unsigned nid = qexpand[i];
thread_temp[tid][nid].Clear();
}
}
const std::vector<bst_uint> &rowset = fmat.buffered_rowset();
// setup position
const bst_omp_uint ndata = static_cast<bst_omp_uint>(rowset.size());
#pragma omp parallel for schedule(static)
for (bst_omp_uint i = 0; i < ndata; ++i) {
const bst_uint ridx = rowset[i];
const int nid = position[ridx];
const int tid = omp_get_thread_num();
if (nid >= 0) {
thread_temp[tid][nid].Add(gpair, info, ridx);
}
}
// sum the per thread statistics together
for (size_t j = 0; j < qexpand.size(); ++j) {
const int nid = qexpand[j];
TStats &s = (*p_node_stats)[nid];
s.Clear();
for (size_t tid = 0; tid < thread_temp.size(); ++tid) {
s.Add(thread_temp[tid][nid]);
}
}
}
/*! \brief common helper data structure to build sketch */
struct SketchEntry {
/*! \brief total sum of amount to be met */
double sum_total;
/*! \brief statistics used in the sketch */
double rmin, wmin;
/*! \brief last seen feature value */
bst_float last_fvalue;
/*! \brief current size of sketch */
double next_goal;
// pointer to the sketch to put things in
common::WXQuantileSketch<bst_float, bst_float> *sketch;
// initialize the space
inline void Init(unsigned max_size) {
next_goal = -1.0f;
rmin = wmin = 0.0f;
sketch->temp.Reserve(max_size + 1);
sketch->temp.size = 0;
}
/*!
* \brief push a new element to sketch
* \param fvalue feature value, comes in sorted ascending order
* \param w weight
* \param max_size
*/
inline void Push(bst_float fvalue, bst_float w, unsigned max_size) {
if (next_goal == -1.0f) {
next_goal = 0.0f;
last_fvalue = fvalue;
wmin = w;
return;
}
if (last_fvalue != fvalue) {
double rmax = rmin + wmin;
if (rmax >= next_goal && sketch->temp.size != max_size) {
if (sketch->temp.size == 0 ||
last_fvalue > sketch->temp.data[sketch->temp.size-1].value) {
// push to sketch
sketch->temp.data[sketch->temp.size] =
common::WXQuantileSketch<bst_float, bst_float>::
Entry(static_cast<bst_float>(rmin),
static_cast<bst_float>(rmax),
static_cast<bst_float>(wmin), last_fvalue);
CHECK_LT(sketch->temp.size, max_size)
<< "invalid maximum size max_size=" << max_size
<< ", stemp.size" << sketch->temp.size;
++sketch->temp.size;
}
if (sketch->temp.size == max_size) {
next_goal = sum_total * 2.0f + 1e-5f;
} else {
next_goal = static_cast<bst_float>(sketch->temp.size * sum_total / max_size);
}
} else {
if (rmax >= next_goal) {
LOG(TRACKER) << "INFO: rmax=" << rmax
<< ", sum_total=" << sum_total
<< ", naxt_goal=" << next_goal
<< ", size=" << sketch->temp.size;
}
}
rmin = rmax;
wmin = w;
last_fvalue = fvalue;
} else {
wmin += w;
}
}
/*! \brief push final unfinished value to the sketch */
inline void Finalize(unsigned max_size) {
double rmax = rmin + wmin;
if (sketch->temp.size == 0 || last_fvalue > sketch->temp.data[sketch->temp.size-1].value) {
CHECK_LE(sketch->temp.size, max_size)
<< "Finalize: invalid maximum size, max_size=" << max_size
<< ", stemp.size=" << sketch->temp.size;
// push to sketch
sketch->temp.data[sketch->temp.size] =
common::WXQuantileSketch<bst_float, bst_float>::
Entry(static_cast<bst_float>(rmin),
static_cast<bst_float>(rmax),
static_cast<bst_float>(wmin), last_fvalue);
++sketch->temp.size;
}
sketch->PushTemp();
}
};
/*! \brief training parameter of tree grower */
TrainParam param;
/*! \brief queue of nodes to be expanded */
std::vector<int> qexpand;
/*!
* \brief map active node to is working index offset in qexpand,
* can be -1, which means the node is node actively expanding
*/
std::vector<int> node2workindex;
/*!
* \brief position of each instance in the tree
* can be negative, which means this position is no longer expanding
* see also Decode/EncodePosition
*/
std::vector<int> position;
private:
inline void UpdateNode2WorkIndex(const RegTree &tree) {
// update the node2workindex
std::fill(node2workindex.begin(), node2workindex.end(), -1);
node2workindex.resize(tree.param.num_nodes);
for (size_t i = 0; i < qexpand.size(); ++i) {
node2workindex[qexpand[i]] = static_cast<int>(i);
}
}
};
} // namespace tree
} // namespace xgboost
#endif // XGBOOST_TREE_UPDATER_BASEMAKER_INL_H_
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