diff --git a/.gitignore b/.gitignore
index 35061b857..48e3a9400 100644
--- a/.gitignore
+++ b/.gitignore
@@ -57,4 +57,3 @@ R-package.Rproj
 *.cache*
 R-package/inst
 R-package/src
-
diff --git a/src/io/page_dmatrix-inl.hpp b/src/io/page_dmatrix-inl.hpp
index 73a3087fb..eb56bb80d 100644
--- a/src/io/page_dmatrix-inl.hpp
+++ b/src/io/page_dmatrix-inl.hpp
@@ -1,7 +1,7 @@
-#ifndef XGBOOST_IO_PAGE_ROW_ITER_INL_HPP_
-#define XGBOOST_IO_PAGE_ROW_ITER_INL_HPP_
+#ifndef XGBOOST_IO_PAGE_DMATRIX_INL_HPP_
+#define XGBOOST_IO_PAGE_DMATRIX_INL_HPP_
 /*!
- * \file page_row_iter-inl.hpp
+ * \file page_dmatrix-inl.hpp
  *   row iterator based on sparse page
  * \author Tianqi Chen
  */
@@ -10,97 +10,11 @@
 #include "../utils/iterator.h"
 #include "../utils/thread_buffer.h"
 #include "./simple_fmatrix-inl.hpp"
+#include "./sparse_batch_page.h"
+#include "./page_fmatrix-inl.hpp"
 
 namespace xgboost {
 namespace io {
-/*! \brief page structure that can be used to store a rowbatch */
-struct RowBatchPage {
- public:
-  explicit RowBatchPage(size_t page_size) : kPageSize(page_size) {
-    data_ = new int[kPageSize];
-    utils::Assert(data_ != NULL, "fail to allocate row batch page");
-    this->Clear();
-  }
-  ~RowBatchPage(void) {
-    if (data_ != NULL) delete [] data_;
-  }
-  /*! 
-   * \brief Push one row into page
-   *  \param row an instance row
-   *  \return false or true to push into
-   */  
-  inline bool PushRow(const RowBatch::Inst &row) {
-    const size_t dsize = row.length * sizeof(RowBatch::Entry);
-    if (FreeBytes() < dsize+ sizeof(int)) return false;
-    row_ptr(Size() + 1) = row_ptr(Size()) + row.length;
-    memcpy(data_ptr(row_ptr(Size())) , row.data, dsize);
-    ++data_[0];
-    return true;
-  }
-  /*!
-   * \brief get a row batch representation from the page
-   * \param p_rptr a temporal space that can be used to provide
-   *  ind_ptr storage for RowBatch
-   * \return a new RowBatch object
-   */
-  inline RowBatch GetRowBatch(std::vector<size_t> *p_rptr, size_t base_rowid) {
-    RowBatch batch;
-    batch.base_rowid = base_rowid;
-    batch.data_ptr = this->data_ptr(0);
-    batch.size = static_cast<size_t>(this->Size());
-    std::vector<size_t> &rptr = *p_rptr;
-    rptr.resize(this->Size() + 1);
-    for (size_t i = 0; i < rptr.size(); ++i) {
-      rptr[i] = static_cast<size_t>(this->row_ptr(static_cast<int>(i)));
-    }
-    batch.ind_ptr = &rptr[0];
-    return batch;
-  }
-  /*! \brief get i-th row from the batch */
-  inline RowBatch::Inst operator[](int i) {
-    return RowBatch::Inst(data_ptr(0) + row_ptr(i),
-                          static_cast<bst_uint>(row_ptr(i+1) - row_ptr(i)));
-  }
-  /*!
-   * \brief clear the page, cleanup the content
-   */
-  inline void Clear(void) {
-    memset(&data_[0], 0, sizeof(int) * kPageSize);
-  }
-  /*!
-   * \brief load one page form instream
-   * \return true if loading is successful
-   */
-  inline bool Load(utils::IStream &fi) {
-    return fi.Read(&data_[0], sizeof(int) * kPageSize) != 0;
-  }
-  /*! \brief save one page into outstream */
-  inline void Save(utils::IStream &fo) {
-    fo.Write(&data_[0], sizeof(int) * kPageSize);
-  }
-  /*! \return number of elements */
-  inline int Size(void) const {
-    return data_[0];
-  }
-
- protected:
-  /*! \return number of elements */
-  inline size_t FreeBytes(void) {
-    return (kPageSize - (Size() + 2)) * sizeof(int) -
-        row_ptr(Size()) * sizeof(RowBatch::Entry);
-  }
-  /*! \brief equivalent row pointer at i */
-  inline int& row_ptr(int i) {
-    return data_[kPageSize - i - 1];
-  }
-  inline RowBatch::Entry* data_ptr(int i) {
-    return (RowBatch::Entry*)(&data_[1]) + i;
-  }
-  // content of data
-  int *data_;
-  // page size
-  const size_t kPageSize;
-};
 /*! \brief thread buffer iterator */
 class ThreadRowPageIterator: public utils::IIterator<RowBatch> {
  public:
@@ -118,7 +32,10 @@ class ThreadRowPageIterator: public utils::IIterator<RowBatch> {
   }
   virtual bool Next(void) {
     if (!itr.Next(page_)) return false;
-    out_ = page_->GetRowBatch(&tmp_ptr_, base_rowid_);
+    out_.base_rowid  = base_rowid_;
+    out_.ind_ptr = BeginPtr(page_->offset);
+    out_.data_ptr = BeginPtr(page_->data);
+    out_.size = page_->offset.size() - 1;
     base_rowid_ += out_.size;
     return true;
   }
@@ -127,76 +44,18 @@ class ThreadRowPageIterator: public utils::IIterator<RowBatch> {
   }
   /*! \brief load and initialize the iterator with fi */
   inline void Load(const utils::FileStream &fi) {
-    itr.get_factory().SetFile(fi);
+    itr.get_factory().SetFile(fi, 0);
     itr.Init();
     this->BeforeFirst();
   }
-  /*!
-   * \brief save a row iterator to output stream, in row iterator format
-   */
-  inline static void Save(utils::IIterator<RowBatch> *iter,
-                          utils::IStream &fo) {
-    RowBatchPage page(kPageSize);
-    iter->BeforeFirst();
-    while (iter->Next()) {
-      const RowBatch &batch = iter->Value();
-      for (size_t i = 0; i < batch.size; ++i) {
-        if (!page.PushRow(batch[i])) {
-          page.Save(fo);
-          page.Clear();
-          utils::Check(page.PushRow(batch[i]), "row is too big");
-        }
-      }
-    }
-    if (page.Size() != 0) page.Save(fo);
-  }
-  /*! \brief page size 64 MB */
-  static const size_t kPageSize = 64 << 18;
 
  private:
   // base row id
   size_t base_rowid_;
-  // temporal ptr
-  std::vector<size_t> tmp_ptr_;
   // output data
   RowBatch out_;
-  // page pointer type
-  typedef RowBatchPage* PagePtr;
-  // loader factory for page
-  struct Factory {
-   public:
-    size_t file_begin_;
-    utils::FileStream fi;
-    Factory(void) {}
-    inline void SetFile(const utils::FileStream &fi) {
-      this->fi = fi;
-      file_begin_ = this->fi.Tell();
-    }
-    inline bool Init(void) {
-      return true;
-    }
-    inline void SetParam(const char *name, const char *val) {}
-    inline bool LoadNext(PagePtr &val) {
-      return val->Load(fi);
-    }
-    inline PagePtr Create(void) {
-      PagePtr a = new RowBatchPage(kPageSize);
-      return a;
-    }
-    inline void FreeSpace(PagePtr &a) {
-      delete a;
-    }
-    inline void Destroy(void) {
-      fi.Close();
-    }
-    inline void BeforeFirst(void) {
-      fi.Seek(file_begin_);
-    }
-  };
-
- protected:
-  PagePtr page_;
-  utils::ThreadBuffer<PagePtr, Factory> itr;
+  SparsePage *page_;
+  utils::ThreadBuffer<SparsePage*, SparsePageFactory> itr;
 };
 
 /*! \brief data matrix using page */
@@ -247,8 +106,20 @@ class DMatrixPageBase : public DataMatrix {
     mat.info.SaveBinary(fs);
     fs.Close();
     fname += ".row.blob";
+    utils::IIterator<RowBatch> *iter = mat.fmat()->RowIterator();
     utils::FileStream fbin(utils::FopenCheck(fname.c_str(), "wb"));
-    ThreadRowPageIterator::Save(mat.fmat()->RowIterator(), fbin);
+    SparsePage page;
+    iter->BeforeFirst();
+    while (iter->Next()) {
+      const RowBatch &batch = iter->Value();
+      for (size_t i = 0; i < batch.size; ++i) {
+        page.Push(batch[i]);
+        if (page.MemCostBytes() >= kPageSize) {
+          page.Save(&fbin); page.Clear();
+        }
+      }
+    }
+    if (page.data.size() != 0) page.Save(&fbin);
     fbin.Close();
     if (!silent) {
       utils::Printf("DMatrixPage: %lux%lu is saved to %s\n",
@@ -268,7 +139,7 @@ class DMatrixPageBase : public DataMatrix {
     }
     std::string fname_row = std::string(cache_file) + ".row.blob";
     utils::FileStream fo(utils::FopenCheck(fname_row.c_str(), "wb"));
-    RowBatchPage page(ThreadRowPageIterator::kPageSize);
+    SparsePage page;
     dmlc::InputSplit *in =
         dmlc::InputSplit::Create(uri, rank, npart);
     std::string line;
@@ -286,10 +157,9 @@ class DMatrixPageBase : public DataMatrix {
         feats.push_back(e);
       }
       RowBatch::Inst row(BeginPtr(feats), feats.size());
-      if (!page.PushRow(row)) {
-        page.Save(fo);
-        page.Clear();
-        utils::Check(page.PushRow(row), "row is too big");
+      page.Push(row);
+      if (page.MemCostBytes() >= kPageSize) {
+        page.Save(&fo); page.Clear();
       }
       for (size_t i = 0; i < feats.size(); ++i) {
         info.info.num_col = std::max(info.info.num_col,
@@ -298,8 +168,8 @@ class DMatrixPageBase : public DataMatrix {
       this->info.labels.push_back(label);
       info.info.num_row += 1;
     }
-    if (page.Size() != 0) {
-      page.Save(fo);
+    if (page.data.size() != 0) {
+      page.Save(&fo);
     }
     delete in;
     fo.Close();    
@@ -319,7 +189,8 @@ class DMatrixPageBase : public DataMatrix {
   }
   /*! \brief magic number used to identify DMatrix */
   static const int kMagic = TKMagic;
-
+  /*! \brief page size 64 MB */
+  static const size_t kPageSize = 64 << 18;
  protected:
   /*! \brief row iterator */
   ThreadRowPageIterator *iter_;
diff --git a/src/io/page_fmatrix-inl.hpp b/src/io/page_fmatrix-inl.hpp
new file mode 100644
index 000000000..44643c329
--- /dev/null
+++ b/src/io/page_fmatrix-inl.hpp
@@ -0,0 +1,130 @@
+#ifndef XGBOOST_IO_PAGE_FMATRIX_INL_HPP_
+#define XGBOOST_IO_PAGE_FMATRIX_INL_HPP_
+/*!
+ * \file page_fmatrix-inl.hpp
+ *   col iterator based on sparse page
+ * \author Tianqi Chen
+ */
+namespace xgboost {
+namespace io {
+/*! \brief thread buffer iterator */
+class ThreadColPageIterator: public utils::IIterator<ColBatch> {
+ public:
+  ThreadColPageIterator(void) {
+    itr.SetParam("buffer_size", "2");
+    page_ = NULL;
+  }
+  virtual ~ThreadColPageIterator(void) {}
+  virtual void Init(void) {}
+  virtual void BeforeFirst(void) {
+    itr.BeforeFirst();
+  }
+  virtual bool Next(void) {
+    if (!itr.Next(page_)) return false;
+    out_.col_index = BeginPtr(itr.get_factory().index_set());
+    col_data_.resize(page_->offset.size() - 1, SparseBatch::Inst(NULL, 0));
+    for (size_t i = 0; i < col_data_.size(); ++i) {
+      col_data_[i] = SparseBatch::Inst
+          (BeginPtr(page_->data) + page_->offset[i],
+           page_->offset[i + 1] - page_->offset[i]);
+    }
+    out_.col_data = BeginPtr(col_data_);
+    out_.size = col_data_.size();
+    return true;
+  }
+  virtual const ColBatch &Value(void) const {
+    return out_;
+  }
+  /*! \brief load and initialize the iterator with fi */
+  inline void SetFile(const utils::FileStream &fi) {
+    itr.get_factory().SetFile(fi, 0);
+    itr.Init();
+  }
+  // set index set
+  inline void SetIndexSet(const std::vector<bst_uint> &fset) {
+    itr.get_factory().SetIndexSet(fset);
+  }
+  
+ private:
+  // output data
+  ColBatch out_;
+  SparsePage *page_;
+  std::vector<SparseBatch::Inst> col_data_;
+  utils::ThreadBuffer<SparsePage*, SparsePageFactory> itr;
+};
+/*!
+ * \brief sparse matrix that support column access, CSC
+ */
+class FMatrixS : public IFMatrix {
+ public:
+  typedef SparseBatch::Entry Entry;
+  /*! \brief constructor */
+  FMatrixS(utils::IIterator<RowBatch> *iter) {
+    this->iter_ = iter;
+  }
+  // destructor
+  virtual ~FMatrixS(void) {
+    if (iter_ != NULL) delete iter_;
+  }
+  /*! \return whether column access is enabled */
+  virtual bool HaveColAccess(void) const {
+    return col_ptr_.size() != 0;
+  }
+  /*! \brief get number of colmuns */
+  virtual size_t NumCol(void) const {
+    utils::Check(this->HaveColAccess(), "NumCol:need column access");
+    return col_ptr_.size() - 1;
+  }
+  /*! \brief get number of buffered rows */
+  virtual const std::vector<bst_uint> &buffered_rowset(void) const {
+    return buffered_rowset_;
+  }
+  /*! \brief get column size */
+  virtual size_t GetColSize(size_t cidx) const {
+    return col_ptr_[cidx+1] - col_ptr_[cidx];
+  }
+  /*! \brief get column density */
+  virtual float GetColDensity(size_t cidx) const {
+    size_t nmiss = buffered_rowset_.size() - (col_ptr_[cidx+1] - col_ptr_[cidx]);
+    return 1.0f - (static_cast<float>(nmiss)) / buffered_rowset_.size();
+  }
+  virtual void InitColAccess(const std::vector<bool> &enabled, 
+                             float pkeep = 1.0f) {
+    if (this->HaveColAccess()) return;
+    this->InitColData(pkeep, enabled);
+  }
+  /*!
+   * \brief get the row iterator associated with FMatrix
+   */
+  virtual utils::IIterator<RowBatch>* RowIterator(void) {
+    iter_->BeforeFirst();
+    return iter_;
+  }
+  /*!
+   * \brief get the column based  iterator
+   */
+  virtual utils::IIterator<ColBatch>* ColIterator(void) {
+    size_t ncol = this->NumCol();
+    col_iter_.col_index_.resize(ncol);
+    for (size_t i = 0; i < ncol; ++i) {
+      col_iter_.col_index_[i] = static_cast<bst_uint>(i);
+    }
+    col_iter_.SetBatch(col_ptr_, col_data_);
+    return &col_iter_;
+  }
+  /*!
+   * \brief colmun based iterator
+   */
+  virtual utils::IIterator<ColBatch> *ColIterator(const std::vector<bst_uint> &fset) {
+    size_t ncol = this->NumCol();
+    col_iter_.col_index_.resize(0);
+    for (size_t i = 0; i < fset.size(); ++i) {
+      if (fset[i] < ncol) col_iter_.col_index_.push_back(fset[i]); 
+    }
+    col_iter_.SetBatch(col_ptr_, col_data_);
+    return &col_iter_;
+  }
+};
+}  // namespace io
+}  // namespace xgboost
+#endif  // XGBOOST_IO_PAGE_FMATRIX_INL_HPP_
diff --git a/src/io/simple_fmatrix-inl.hpp b/src/io/simple_fmatrix-inl.hpp
index 9f204536f..3ba6f2801 100644
--- a/src/io/simple_fmatrix-inl.hpp
+++ b/src/io/simple_fmatrix-inl.hpp
@@ -16,7 +16,7 @@ namespace io {
 /*!
  * \brief sparse matrix that support column access, CSC
  */
-class FMatrixS : public IFMatrix{
+class FMatrixS : public IFMatrix {
  public:
   typedef SparseBatch::Entry Entry;
   /*! \brief constructor */
@@ -238,7 +238,7 @@ class FMatrixS : public IFMatrix{
     inline void SetBatch(const std::vector<size_t> &ptr,
                          const std::vector<ColBatch::Entry> &data) {
       batch_.size = col_index_.size();
-      col_data_.resize(col_index_.size(), SparseBatch::Inst(NULL,0));
+      col_data_.resize(col_index_.size(), SparseBatch::Inst(NULL, 0));
       for (size_t i = 0; i < col_data_.size(); ++i) {
         const bst_uint ridx = col_index_[i];
         col_data_[i] = SparseBatch::Inst(&data[0] + ptr[ridx],
diff --git a/src/io/sparse_batch_page.h b/src/io/sparse_batch_page.h
new file mode 100644
index 000000000..f7bbb08de
--- /dev/null
+++ b/src/io/sparse_batch_page.h
@@ -0,0 +1,216 @@
+#ifndef XGBOOST_IO_SPARSE_BATCH_PAGE_H_
+#define XGBOOST_IO_SPARSE_BATCH_PAGE_H_
+/*!
+ * \file sparse_batch_page.h
+ *   content holder of sparse batch that can be saved to disk
+ *   the representation can be effectively
+ *   use in external memory computation
+ * \author Tianqi Chen
+ */
+#include "../data.h"
+
+namespace xgboost {
+namespace io {
+/*!
+ * \brief storage unit of sparse batch  
+ */
+class SparsePage {
+ public:
+  /*! \brief offset of the segments */
+  std::vector<size_t> offset;
+  /*! \brief the data of the segments */
+  std::vector<SparseBatch::Entry> data;
+  /*! \brief constructor */
+  SparsePage() {
+    this->Clear();
+  }
+  /*!
+   * \brief load the by providing a list of interested segments
+   *        only the interested segments are loaded
+   * \param fi the input stream of the file
+   * \param sorted_index_set sorted index of segments we are interested in
+   * \return true of the loading as successful, false if end of file was reached
+   */
+  inline bool Load(utils::ISeekStream *fi,
+                   const std::vector<bst_uint> &sorted_index_set) {
+    if (!fi->Read(&disk_offset_)) return false;
+    // setup the offset
+    offset.clear(); offset.push_back(0);
+    for (size_t i = 0; i < sorted_index_set.size(); ++i) {
+      bst_uint fid = sorted_index_set[i];
+      size_t size = disk_offset_[fid + 1] - disk_offset_[fid];
+      offset.push_back(offset.back() + size);
+    }
+    data.resize(offset.back());
+    // read in the data
+    size_t begin = fi->Tell();
+    size_t curr_offset = 0;
+    for (size_t i = 0; i < sorted_index_set.size();) {
+      bst_uint fid = sorted_index_set[i];
+      if (disk_offset_[fid] != curr_offset) {
+        utils::Assert(disk_offset_[fid] > curr_offset, "fset index was not sorted");
+        fi->Seek(begin + disk_offset_[fid]);
+        curr_offset = disk_offset_[fid];
+      }
+      size_t j, size_to_read = 0;
+      for (j = i; j < sorted_index_set.size(); ++j) {
+        if (disk_offset_[sorted_index_set[j]] == disk_offset_[fid] + size_to_read) {
+          size_to_read += offset[j + 1] - offset[j];
+        } else {
+          break;
+        }
+      }
+      if (size_to_read != 0) {
+        utils::Check(fi->Read(BeginPtr(data) + offset[i],
+                              size_to_read * sizeof(SparseBatch::Entry)) != 0,
+                     "Invalid SparsePage file");
+        curr_offset += size_to_read;
+      }
+      i = j;
+    }
+    return true;
+  }
+  /*!
+   * \brief load all the segments
+   * \param fi the input stream of the file
+   * \return true of the loading as successful, false if end of file was reached
+   */
+  inline bool Load(utils::IStream *fi) {
+    if (!fi->Read(&offset)) return false;
+    utils::Check(offset.size() != 0, "Invalid SparsePage file");
+    data.resize(offset.back());
+    if (data.size() != 0) {
+      utils::Check(fi->Read(BeginPtr(data), data.size() * sizeof(SparseBatch::Entry)) != 0,
+                   "Invalid SparsePage file");
+    }
+    return true;
+  }
+  /*!
+   * \brief save the data to fo, when a page was written
+   *    to disk it must contain all the elements in the 
+   * \param fo output stream
+   */
+  inline void Save(utils::IStream *fo) const {
+    utils::Assert(offset.size() != 0 && offset[0] == 0, "bad offset");
+    utils::Assert(offset.back() == data.size(), "in consistent SparsePage");
+    fo->Write(offset);
+    if (data.size() != 0) {
+      fo->Write(BeginPtr(data), data.size() * sizeof(SparseBatch::Entry));
+    }
+  }
+  /*! \return estimation of memory cost of this page */
+  inline size_t MemCostBytes(void) const {
+    return offset.size() * sizeof(size_t) + data.size() * sizeof(SparseBatch::Entry);
+  }
+  /*! \brief clear the page */
+  inline void Clear(void) {
+    offset.clear();
+    offset.push_back(0);
+    data.clear();
+  }
+  /*!
+   * \brief load all the segments and add it to existing batch
+   * \param fi the input stream of the file
+   * \return true of the loading as successful, false if end of file was reached
+   */
+  inline bool PushLoad(utils::IStream *fi) {
+    if (!fi->Read(&disk_offset_)) return false;
+    data.resize(offset.back() + disk_offset_.back());    
+    if (disk_offset_.back() != 0) {
+      utils::Check(fi->Read(BeginPtr(data) + offset.back(),
+                            disk_offset_.back() * sizeof(SparseBatch::Entry)) != 0,
+                   "Invalid SparsePage file");
+    }
+    size_t top = offset.back();
+    size_t begin = offset.size();
+    offset.resize(offset.size() + disk_offset_.size());
+    for (size_t i = 0; i < disk_offset_.size(); ++i) {
+      offset[i + begin] = top + disk_offset_[i];
+    }
+  }
+  /*! 
+   * \brief Push row batch into the page
+   * \param batch the row batch
+   */
+  inline void Push(const RowBatch &batch) {
+    data.resize(offset.back() + batch.size);
+    std::memcpy(BeginPtr(data) + offset.back(),
+                batch.data_ptr + batch.ind_ptr[0],
+                sizeof(SparseBatch::Entry) * batch.ind_ptr[batch.size]);
+    size_t top = offset.back();
+    size_t begin = offset.size();
+    offset.resize(offset.size() + batch.size);
+    for (size_t i = 0; i < batch.size; ++i) {
+      offset[i + begin] = top + batch.ind_ptr[i] - batch.ind_ptr[0];
+    }
+  }
+  /*! 
+   * \brief Push one instance into page
+   *  \param row an instance row
+   */
+  inline void Push(const SparseBatch::Inst &inst) {
+    offset.push_back(offset.back() + inst.length);
+    size_t begin = data.size();
+    data.resize(begin + inst.length);
+    std::memcpy(BeginPtr(data) + begin, inst.data,
+                sizeof(SparseBatch::Entry) * inst.length);
+  }
+
+ private:
+  /*! \brief external memory column offset */
+  std::vector<size_t> disk_offset_;
+};
+/*!
+ * \brief factory class for SparsePage,
+ *        used in threadbuffer template  
+ */
+class SparsePageFactory {
+ public:
+  SparsePageFactory(void) {}
+  inline void SetFile(const utils::FileStream &fi,
+                      size_t file_begin = 0) {
+    fi_ = fi;
+    file_begin_ = file_begin;
+  }
+  inline const std::vector<bst_uint> &index_set(void) const {
+    return action_index_set_;
+  }
+  // set index set, will be used after next before first
+  inline void SetIndexSet(const std::vector<bst_uint> &index_set) {
+    set_index_set_ = index_set;
+    std::sort(set_index_set_.begin(), set_index_set_.end());
+  }
+  inline bool Init(void) {
+    return true;
+  }
+  inline void SetParam(const char *name, const char *val) {}
+  inline bool LoadNext(SparsePage *val) {
+    if (action_index_set_.size() != 0) {
+      return val->Load(&fi_, action_index_set_);
+    } else {
+      return val->Load(&fi_);      
+    }
+  }
+  inline SparsePage *Create(void) {
+    return new SparsePage();
+  }
+  inline void FreeSpace(SparsePage *a) {
+    delete a;
+  }
+  inline void Destroy(void) {
+    fi_.Close();
+  }
+  inline void BeforeFirst(void) {
+    fi_.Seek(file_begin_);
+    action_index_set_ = set_index_set_;
+  }
+
+ private:
+  size_t file_begin_;
+  utils::FileStream fi_;
+  std::vector<bst_uint> action_index_set_;
+  std::vector<bst_uint> set_index_set_;
+};
+}  // namespace io
+}  // namespace xgboost
+#endif  // XGBOOST_IO_SPARSE_BATCH_PAGE_H_