From d08d8ed3edbc7c5c80ec0f1d72e3b806976d03ad Mon Sep 17 00:00:00 2001
From: tqchen <tianqi.tchen@gmail.com>
Date: Mon, 18 Aug 2014 21:32:48 -0700
Subject: [PATCH] add tree refresher, need review

---
 src/tree/updater_refresh-inl.hpp | 138 +++++++++++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 src/tree/updater_refresh-inl.hpp

diff --git a/src/tree/updater_refresh-inl.hpp b/src/tree/updater_refresh-inl.hpp
new file mode 100644
index 000000000..69f099e1d
--- /dev/null
+++ b/src/tree/updater_refresh-inl.hpp
@@ -0,0 +1,138 @@
+#ifndef XGBOOST_TREE_UPDATER_REFRESH_INL_HPP_
+#define XGBOOST_TREE_UPDATER_REFRESH_INL_HPP_
+/*!
+ * \file updater_refresh-inl.hpp
+ * \brief refresh the statistics and leaf value on the tree on the dataset
+ * \author Tianqi Chen
+ */
+#include <vector>
+#include <limits>
+#include "./param.h"
+#include "./updater.h"
+
+namespace xgboost {
+namespace tree {
+/*! \brief pruner that prunes a tree after growing finishs */
+template<typename FMatrix>
+class TreeRefresher: public IUpdater<FMatrix> {
+ public:
+  virtual ~TreeRefresher(void) {}
+  // set training parameter
+  virtual void SetParam(const char *name, const char *val) {
+    param.SetParam(name, val);
+    if (!strcmp(name, "silent")) silent = atoi(val);
+  }
+  // update the tree, do pruning
+  virtual void Update(const std::vector<bst_gpair> &gpair,
+                      const FMatrix &fmat,
+                      const std::vector<unsigned> &root_index,
+                      const std::vector<RegTree*> &trees) {
+    if (trees.size() == 0) return;
+    // number of threads
+    int nthread;
+    // thread temporal space
+    std::vector< std::vector<GradStats> > stemp;
+    std::vector<RegTree::FVec> fvec_temp;
+    // setup temp space for each thread
+    #pragma omp parallel
+    {
+      nthread = omp_get_num_threads();
+    }
+    fvec_temp.resize(nthread, RegTree::FVec());
+    stemp.resize(trees.size() * nthread, std::vector<GradStats>());
+    #pragma omp parallel
+    {
+      int tid = omp_get_thread_num();
+      for (size_t i = 0; i < trees.size(); ++i) {
+        std::vector<GradStats> &vec = stemp[tid * trees.size() + i];
+        vec.resize(trees[i]->param.num_nodes);
+        std::fill(vec.begin(), vec.end(), GradStats());
+      }
+      fvec_temp[tid].Init(trees[0]->param.num_feature);
+    }
+    // start accumulating statistics
+    utils::IIterator<SparseBatch> *iter = fmat.RowIterator();
+    iter->BeforeFirst();
+    while (iter->Next()) {
+      const SparseBatch &batch = iter->Value();
+      utils::Check(batch.size < std::numeric_limits<unsigned>::max(),
+                   "too large batch size ");
+      const unsigned nbatch = static_cast<unsigned>(batch.size);
+      #pragma omp parallel for schedule(static)
+      for (unsigned i = 0; i < nbatch; ++i) {
+        SparseBatch::Inst inst = batch[i];
+        const int tid = omp_get_thread_num();
+        const size_t ridx = batch.base_rowid + i;
+        RegTree::FVec &feats = fvec_temp[tid];
+        feats.Fill(inst);
+        for (size_t j = 0; j < trees.size(); ++j) {
+          AddStats(*trees[j], feats, gpair[ridx],
+                   root_index.size() == 0 ? 0 : root_index[ridx],
+                   &stemp[tid * trees.size() + j]);
+        }
+        feats.Drop(inst);
+      }
+    }
+    // start update the trees using the statistics
+    // rescale learning rate according to size of trees
+    float lr = param.learning_rate;
+    param.learning_rate = lr / trees.size();
+    for (size_t i = 0; i < trees.size(); ++i) {
+      // aggregate
+      #pragma omp parallel for schedule(static)
+      for (int nid = 0; nid < trees[i]->param.num_nodes; ++nid) {
+        for (int tid = 1; tid < nthread; ++tid) {
+          stemp[i][nid].Add(stemp[tid * trees.size() + i][nid]);
+        }
+      }
+      for (int rid = 0; rid < trees[i]->param.num_roots; ++rid) {
+        this->Refresh(stemp[i], rid, trees[i]);
+      }
+    }
+    // set learning rate back
+    param.learning_rate = lr;
+  }
+
+ private:
+  inline static void AddStats(const RegTree &tree,
+                              const RegTree::FVec &feat,
+                              const bst_gpair &gpair, unsigned root_id,
+                              std::vector<GradStats> *p_gstats) {
+    std::vector<GradStats> &gstats = *p_gstats;
+    // start from groups that belongs to current data
+    int pid = static_cast<int>(root_id);
+    gstats[pid].Add(gpair);
+    // tranverse tree
+    while (!tree[pid].is_leaf()) {
+      unsigned split_index = tree[pid].split_index();
+      pid = tree.GetNext(pid, feat.fvalue(split_index), feat.is_missing(split_index));
+      gstats[pid].Add(gpair);
+    }
+  }
+  inline void Refresh(const std::vector<GradStats> &gstats,
+                      int nid, RegTree *p_tree) {
+    RegTree &tree = *p_tree;
+    tree.stat(nid).base_weight = param.CalcWeight(gstats[nid]);
+    tree.stat(nid).sum_hess = static_cast<float>(gstats[nid].sum_hess);
+    if (tree[nid].is_leaf()) {
+      tree[nid].set_leaf(tree.stat(nid).base_weight * param.learning_rate);
+    } else {
+      tree.stat(nid).loss_chg =
+          param.CalcGain(gstats[tree[nid].cleft()]) +
+          param.CalcGain(gstats[tree[nid].cright()]) -
+          param.CalcGain(gstats[nid]);
+      this->Refresh(gstats, tree[nid].cleft(), p_tree);
+      this->Refresh(gstats, tree[nid].cright(), p_tree);
+    }
+  }
+  // number of thread in the data
+  int nthread;
+  // shutup
+  int silent;
+  // training parameter
+  TrainParam param;
+};
+
+}  // namespace tree
+}  // namespace xgboost
+#endif  // XGBOOST_TREE_UPDATER_REFRESH_INL_HPP_