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Fix pruner. (#5335)

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* Honor the tree depth.
* Prevent pruning pruned node.
This commit is contained in:
Jiaming Yuan
2020-02-25 08:32:46 +08:00
committed by GitHub
parent b0ed3f0a66
commit e0509b3307
5 changed files with 99 additions and 34 deletions
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5
src/tree/param.h
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@@ -220,8 +220,9 @@ struct TrainParam : public XGBoostParameter<TrainParam> {
}
/*! \brief given the loss change, whether we need to invoke pruning */
inline bool NeedPrune(double loss_chg, int depth) const {
return loss_chg < this->min_split_loss;
bool NeedPrune(double loss_chg, int depth) const {
return loss_chg < this->min_split_loss ||
(this->max_depth != 0 && depth > this->max_depth);
}
/*! \brief maximum sketch size */
inline unsigned MaxSketchSize() const {

36
src/tree/updater_prune.cc
View File

@@ -1,5 +1,5 @@
/*!
* Copyright 2014 by Contributors
* Copyright 2014-2020 by Contributors
* \file updater_prune.cc
* \brief prune a tree given the statistics
* \author Tianqi Chen
@@ -10,6 +10,7 @@
#include <string>
#include <memory>
#include "xgboost/base.h"
#include "xgboost/json.h"
#include "./param.h"
#include "../common/io.h"
@@ -52,7 +53,7 @@ class TreePruner: public TreeUpdater {
float lr = param_.learning_rate;
param_.learning_rate = lr / trees.size();
for (auto tree : trees) {
this->DoPrune(*tree);
this->DoPrune(tree);
}
param_.learning_rate = lr;
syncher_->Update(gpair, p_fmat, trees);
@@ -60,12 +61,20 @@ class TreePruner: public TreeUpdater {
private:
// try to prune off current leaf
inline int TryPruneLeaf(RegTree &tree, int nid, int depth, int npruned) { // NOLINT(*)
if (tree[nid].IsRoot()) return npruned;
int pid = tree[nid].Parent();
RTreeNodeStat &s = tree.Stat(pid);
++s.leaf_child_cnt;
if (s.leaf_child_cnt >= 2 && param_.NeedPrune(s.loss_chg, depth - 1)) {
bst_node_t TryPruneLeaf(RegTree &tree, int nid, int depth, int npruned) { // NOLINT(*)
CHECK(tree[nid].IsLeaf());
if (tree[nid].IsRoot()) {
return npruned;
}
bst_node_t pid = tree[nid].Parent();
CHECK(!tree[pid].IsLeaf());
RTreeNodeStat const &s = tree.Stat(pid);
// Only prune when both child are leaf.
auto left = tree[pid].LeftChild();
auto right = tree[pid].RightChild();
bool balanced = tree[left].IsLeaf() &&
right != RegTree::kInvalidNodeId && tree[right].IsLeaf();
if (balanced && param_.NeedPrune(s.loss_chg, depth)) {
// need to be pruned
tree.ChangeToLeaf(pid, param_.learning_rate * s.base_weight);
// tail recursion
@@ -75,14 +84,11 @@ class TreePruner: public TreeUpdater {
}
}
/*! \brief do pruning of a tree */
inline void DoPrune(RegTree &tree) { // NOLINT(*)
int npruned = 0;
// initialize auxiliary statistics
void DoPrune(RegTree* p_tree) {
auto& tree = *p_tree;
bst_node_t npruned = 0;
for (int nid = 0; nid < tree.param.num_nodes; ++nid) {
tree.Stat(nid).leaf_child_cnt = 0;
}
for (int nid = 0; nid < tree.param.num_nodes; ++nid) {
if (tree[nid].IsLeaf()) {
if (tree[nid].IsLeaf() && !tree[nid].IsDeleted()) {
npruned = this->TryPruneLeaf(tree, nid, tree.GetDepth(nid), npruned);
}
}