remove the qids_ field in MetaInfo (#4744)

include/xgboost/data.h

@@ -60,8 +60,6 @@ class MetaInfo {
   std::vector<bst_uint> group_ptr_;
   /*! \brief weights of each instance, optional */
   HostDeviceVector<bst_float> weights_;
-  /*! \brief session-id of each instance, optional */
-  std::vector<uint64_t> qids_;
   /*!
    * \brief initialized margins,
    * if specified, xgboost will start from this init margin
@@ -69,9 +67,9 @@ class MetaInfo {
    */
   HostDeviceVector<bst_float> base_margin_;
   /*! \brief version flag, used to check version of this info */
-  static const int kVersion = 2;
+  static const int kVersion = 3;
-  /*! \brief version that introduced qid field */
+  /*! \brief version that contains qid field */
-  static const int kVersionQidAdded = 2;
+  static const int kVersionWithQid = 2;
   /*! \brief default constructor */
   MetaInfo()  = default;
   /*!

src/data/data.cc

@@ -27,7 +27,6 @@ void MetaInfo::Clear() {
   labels_.HostVector().clear();
   root_index_.clear();
   group_ptr_.clear();
-  qids_.clear();
   weights_.HostVector().clear();
   base_margin_.HostVector().clear();
 }
@@ -40,7 +39,6 @@ void MetaInfo::SaveBinary(dmlc::Stream *fo) const {
   fo->Write(&num_nonzero_, sizeof(num_nonzero_));
   fo->Write(labels_.HostVector());
   fo->Write(group_ptr_);
-  fo->Write(qids_);
   fo->Write(weights_.HostVector());
   fo->Write(root_index_);
   fo->Write(base_margin_.HostVector());
@@ -56,10 +54,9 @@ void MetaInfo::LoadBinary(dmlc::Stream *fi) {
       << "MetaInfo: invalid format";
   CHECK(fi->Read(&labels_.HostVector())) <<  "MetaInfo: invalid format";
   CHECK(fi->Read(&group_ptr_)) << "MetaInfo: invalid format";
-  if (version >= kVersionQidAdded) {
+  if (version == kVersionWithQid) {
-    CHECK(fi->Read(&qids_)) << "MetaInfo: invalid format";
+    std::vector<uint64_t> qids;
-  } else {  // old format doesn't contain qid field
+    CHECK(fi->Read(&qids)) << "MetaInfo: invalid format";
-    qids_.clear();
   }
   CHECK(fi->Read(&weights_.HostVector())) << "MetaInfo: invalid format";
   CHECK(fi->Read(&root_index_)) << "MetaInfo: invalid format";

src/data/simple_csr_source.cc

@@ -28,6 +28,7 @@ void SimpleCSRSource::CopyFrom(dmlc::Parser<uint32_t>* parser) {
   const uint64_t default_max = std::numeric_limits<uint64_t>::max();
   uint64_t last_group_id = default_max;
   bst_uint group_size = 0;
+  std::vector<uint64_t> qids;
   this->Clear();
   while (parser->Next()) {
     const dmlc::RowBlock<uint32_t>& batch = parser->Value();
@@ -40,7 +41,7 @@ void SimpleCSRSource::CopyFrom(dmlc::Parser<uint32_t>* parser) {
       weights.insert(weights.end(), batch.weight, batch.weight + batch.size);
     }
     if (batch.qid != nullptr) {
-      info.qids_.insert(info.qids_.end(), batch.qid, batch.qid + batch.size);
+      qids.insert(qids.end(), batch.qid, batch.qid + batch.size);
       // get group
       for (size_t i = 0; i < batch.size; ++i) {
         const uint64_t cur_group_id = batch.qid[i];
@@ -82,7 +83,7 @@ void SimpleCSRSource::CopyFrom(dmlc::Parser<uint32_t>* parser) {
   }
   this->info.num_nonzero_ = static_cast<uint64_t>(page_.data.Size());
   // Either every row has query ID or none at all
-  CHECK(info.qids_.empty() || info.qids_.size() == info.num_row_);
+  CHECK(qids.empty() || qids.size() == info.num_row_);
 }
 
 void SimpleCSRSource::LoadBinary(dmlc::Stream* fi) {

src/data/sparse_page_source.h

@@ -172,6 +172,7 @@ class SparsePageSource : public DataSource<T> {
       const uint64_t default_max = std::numeric_limits<uint64_t>::max();
       uint64_t last_group_id = default_max;
       bst_uint group_size = 0;
+      std::vector<uint64_t> qids;
 
       while (src->Next()) {
         const dmlc::RowBlock<uint32_t>& batch = src->Value();
@@ -184,7 +185,7 @@ class SparsePageSource : public DataSource<T> {
           weights.insert(weights.end(), batch.weight, batch.weight + batch.size);
         }
         if (batch.qid != nullptr) {
-          info.qids_.insert(info.qids_.end(), batch.qid, batch.qid + batch.size);
+          qids.insert(qids.end(), batch.qid, batch.qid + batch.size);
           // get group
           for (size_t i = 0; i < batch.size; ++i) {
             const uint64_t cur_group_id = batch.qid[i];
@@ -233,7 +234,7 @@ class SparsePageSource : public DataSource<T> {
       int tmagic = kMagic;
       fo->Write(&tmagic, sizeof(tmagic));
       // Either every row has query ID or none at all
-      CHECK(info.qids_.empty() || info.qids_.size() == info.num_row_);
+      CHECK(qids.empty() || qids.size() == info.num_row_);
       info.SaveBinary(fo.get());
     }
     LOG(INFO) << "SparsePageSource::CreateRowPage Finished writing to "

tests/cpp/data/test_metainfo.cc

@@ -55,7 +55,7 @@ TEST(MetaInfo, SaveLoadBinary) {
   info.SaveBinary(fs);
   delete fs;
 
-  ASSERT_EQ(GetFileSize(tmp_file), 84)
+  ASSERT_EQ(GetFileSize(tmp_file), 76)
     << "Expected saved binary file size to be same as object size";
 
   fs = dmlc::Stream::Create(tmp_file.c_str(), "r");
@@ -92,11 +92,8 @@ TEST(MetaInfo, LoadQid) {
     xgboost::DMatrix::Load(tmp_file, true, false, "libsvm"));
 
   const xgboost::MetaInfo& info = dmat->Info();
-  const std::vector<uint64_t> expected_qids{1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3};
   const std::vector<xgboost::bst_uint> expected_group_ptr{0, 4, 8, 12};
-  CHECK(info.qids_ == expected_qids);
   CHECK(info.group_ptr_ == expected_group_ptr);
-  CHECK_GE(info.kVersion, info.kVersionQidAdded);
 
   const std::vector<size_t> expected_offset{
     0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60