diff --git a/src/common/row_set.h b/src/common/row_set.h
index 11f12bda3..acb397305 100644
--- a/src/common/row_set.h
+++ b/src/common/row_set.h
@@ -1,5 +1,5 @@
-/*!
- * Copyright 2017-2022 by Contributors
+/**
+ * Copyright 2017-2024, XGBoost Contributors
  * \file row_set.h
  * \brief Quick Utility to compute subset of rows
  * \author Philip Cho, Tianqi Chen
@@ -7,15 +7,17 @@
 #ifndef XGBOOST_COMMON_ROW_SET_H_
 #define XGBOOST_COMMON_ROW_SET_H_
 
-#include <xgboost/data.h>
-#include <algorithm>
-#include <vector>
-#include <utility>
-#include <memory>
+#include <cstddef>   // for size_t
+#include <iterator>  // for distance
+#include <vector>    // for vector
 
-namespace xgboost {
-namespace common {
-/*! \brief collection of rowset */
+#include "xgboost/base.h"     // for bst_node_t
+#include "xgboost/logging.h"  // for CHECK
+
+namespace xgboost::common {
+/**
+ * @brief Collection of rows for each tree node.
+ */
 class RowSetCollection {
  public:
   RowSetCollection() = default;
@@ -24,84 +26,78 @@ class RowSetCollection {
   RowSetCollection& operator=(RowSetCollection const&) = delete;
   RowSetCollection& operator=(RowSetCollection&&) = default;
 
-  /*! \brief data structure to store an instance set, a subset of
-   *  rows (instances) associated with a particular node in a decision
-   *  tree. */
+  /**
+   * @brief data structure to store an instance set, a subset of rows (instances)
+   *        associated with a particular node in a decision tree.
+   */
   struct Elem {
-    const size_t* begin{nullptr};
-    const size_t* end{nullptr};
+    std::size_t const* begin{nullptr};
+    std::size_t const* end{nullptr};
     bst_node_t node_id{-1};
-      // id of node associated with this instance set; -1 means uninitialized
-    Elem()
-         = default;
-    Elem(const size_t* begin,
-         const size_t* end,
-         bst_node_t node_id = -1)
+    // id of node associated with this instance set; -1 means uninitialized
+    Elem() = default;
+    Elem(std::size_t const* begin, std::size_t const* end, bst_node_t node_id = -1)
         : begin(begin), end(end), node_id(node_id) {}
 
-    inline size_t Size() const {
-      return end - begin;
-    }
+    std::size_t Size() const { return end - begin; }
   };
 
-  std::vector<Elem>::const_iterator begin() const {  // NOLINT
-    return elem_of_each_node_.begin();
+  [[nodiscard]] std::vector<Elem>::const_iterator begin() const {  // NOLINT
+    return elem_of_each_node_.cbegin();
+  }
+  [[nodiscard]] std::vector<Elem>::const_iterator end() const {  // NOLINT
+    return elem_of_each_node_.cend();
   }
 
-  std::vector<Elem>::const_iterator end() const {  // NOLINT
-    return elem_of_each_node_.end();
-  }
+  [[nodiscard]] std::size_t Size() const { return std::distance(begin(), end()); }
 
-  size_t Size() const { return std::distance(begin(), end()); }
-
-  /*! \brief return corresponding element set given the node_id */
-  inline const Elem& operator[](unsigned node_id) const {
-    const Elem& e = elem_of_each_node_[node_id];
+  /** @brief return corresponding element set given the node_id */
+  [[nodiscard]] Elem const& operator[](bst_node_t node_id) const {
+    Elem const& e = elem_of_each_node_[node_id];
     return e;
   }
-
-  /*! \brief return corresponding element set given the node_id */
-  inline Elem& operator[](unsigned node_id) {
+  /** @brief return corresponding element set given the node_id */
+  [[nodiscard]] Elem& operator[](bst_node_t node_id) {
     Elem& e = elem_of_each_node_[node_id];
     return e;
   }
 
   // clear up things
-  inline void Clear() {
+  void Clear() {
     elem_of_each_node_.clear();
   }
   // initialize node id 0->everything
-  inline void Init() {
-    CHECK_EQ(elem_of_each_node_.size(), 0U);
+  void Init() {
+    CHECK(elem_of_each_node_.empty());
 
     if (row_indices_.empty()) {  // edge case: empty instance set
-      constexpr size_t* kBegin = nullptr;
-      constexpr size_t* kEnd = nullptr;
+      constexpr std::size_t* kBegin = nullptr;
+      constexpr std::size_t* kEnd = nullptr;
       static_assert(kEnd - kBegin == 0);
       elem_of_each_node_.emplace_back(kBegin, kEnd, 0);
       return;
     }
 
-    const size_t* begin = dmlc::BeginPtr(row_indices_);
-    const size_t* end = dmlc::BeginPtr(row_indices_) + row_indices_.size();
+    const std::size_t* begin = dmlc::BeginPtr(row_indices_);
+    const std::size_t* end = dmlc::BeginPtr(row_indices_) + row_indices_.size();
     elem_of_each_node_.emplace_back(begin, end, 0);
   }
 
-  std::vector<size_t>* Data() { return &row_indices_; }
-  std::vector<size_t> const* Data() const { return &row_indices_; }
+  [[nodiscard]] std::vector<std::size_t>* Data() { return &row_indices_; }
+  [[nodiscard]] std::vector<std::size_t> const* Data() const { return &row_indices_; }
 
   // split rowset into two
-  inline void AddSplit(unsigned node_id, unsigned left_node_id, unsigned right_node_id,
-                       size_t n_left, size_t n_right) {
+  void AddSplit(bst_node_t node_id, bst_node_t left_node_id, bst_node_t right_node_id,
+                bst_idx_t n_left, bst_idx_t n_right) {
     const Elem e = elem_of_each_node_[node_id];
 
-    size_t* all_begin{nullptr};
-    size_t* begin{nullptr};
+    std::size_t* all_begin{nullptr};
+    std::size_t* begin{nullptr};
     if (e.begin == nullptr) {
       CHECK_EQ(n_left, 0);
       CHECK_EQ(n_right, 0);
     } else {
-      all_begin = dmlc::BeginPtr(row_indices_);
+      all_begin = row_indices_.data();
       begin = all_begin + (e.begin - all_begin);
     }
 
@@ -109,25 +105,24 @@ class RowSetCollection {
     CHECK_LE(begin + n_left, e.end);
     CHECK_EQ(begin + n_left + n_right, e.end);
 
-    if (left_node_id >= elem_of_each_node_.size()) {
-      elem_of_each_node_.resize(left_node_id + 1, Elem(nullptr, nullptr, -1));
+    if (left_node_id >= static_cast<bst_node_t>(elem_of_each_node_.size())) {
+      elem_of_each_node_.resize(left_node_id + 1, Elem{nullptr, nullptr, -1});
     }
-    if (right_node_id >= elem_of_each_node_.size()) {
-      elem_of_each_node_.resize(right_node_id + 1, Elem(nullptr, nullptr, -1));
+    if (right_node_id >= static_cast<bst_node_t>(elem_of_each_node_.size())) {
+      elem_of_each_node_.resize(right_node_id + 1, Elem{nullptr, nullptr, -1});
     }
 
-    elem_of_each_node_[left_node_id] = Elem(begin, begin + n_left, left_node_id);
-    elem_of_each_node_[right_node_id] = Elem(begin + n_left, e.end, right_node_id);
-    elem_of_each_node_[node_id] = Elem(nullptr, nullptr, -1);
+    elem_of_each_node_[left_node_id] = Elem{begin, begin + n_left, left_node_id};
+    elem_of_each_node_[right_node_id] = Elem{begin + n_left, e.end, right_node_id};
+    elem_of_each_node_[node_id] = Elem{nullptr, nullptr, -1};
   }
 
  private:
   // stores the row indexes in the set
-  std::vector<size_t> row_indices_;
+  std::vector<std::size_t> row_indices_;
   // vector: node_id -> elements
   std::vector<Elem> elem_of_each_node_;
 };
-}  // namespace common
-}  // namespace xgboost
+}  // namespace xgboost::common
 
 #endif  // XGBOOST_COMMON_ROW_SET_H_