Make statistics useful again.

src/mlpack/core/tree/binary_space_tree_impl.hpp

@@ -99,6 +99,12 @@ BinarySpaceTree<BoundType, StatisticType, MatType>::BinarySpaceTree(
 {
   // Perform the actual splitting.
   SplitNode(data);
+
+  // Create the statistic depending on if we are a leaf or not.
+  if (IsLeaf())
+    stat = StatisticType(data, begin, count);
+  else
+    stat = StatisticType(data, begin, count, left->Stat(), right->Stat());
 }
 
 template<typename BoundType, typename StatisticType, typename MatType>
@@ -122,6 +128,12 @@ BinarySpaceTree<BoundType, StatisticType, MatType>::BinarySpaceTree(
 
   // Perform the actual splitting.
   SplitNode(data, oldFromNew);
+
+  // Create the statistic depending on if we are a leaf or not.
+  if (IsLeaf())
+    stat = StatisticType(data, begin, count);
+  else
+    stat = StatisticType(data, begin, count, left->Stat(), right->Stat());
 }
 
 template<typename BoundType, typename StatisticType, typename MatType>
@@ -151,6 +163,12 @@ BinarySpaceTree<BoundType, StatisticType, MatType>::BinarySpaceTree(
   newFromOld.resize(data.n_cols);
   for (size_t i = 0; i < data.n_cols; i++)
     newFromOld[oldFromNew[i]] = i;
+
+  // Create the statistic depending on if we are a leaf or not.
+  if (IsLeaf())
+    stat = StatisticType(data, begin, count);
+  else
+    stat = StatisticType(data, begin, count, left->Stat(), right->Stat());
 }
 
 template<typename BoundType, typename StatisticType, typename MatType>

src/mlpack/core/tree/statistic.hpp

@@ -15,8 +15,6 @@ namespace tree {
 /**
  * Empty statistic if you are not interested in storing statistics in your
  * tree.  Use this as a template for your own.
- *
- * @experimental
  */
 class EmptyStatistic
 {
@@ -25,17 +23,35 @@ class EmptyStatistic
     ~EmptyStatistic() {}
 
     /**
-     * Initializes by taking statistics on raw data.
+     * This constructor is called when a leaf is created.
+     *
+     * @param dataset Matrix that the tree is being built on.
+     * @param begin Starting index corresponding to this leaf.
+     * @param count Number of points held in this leaf.
      */
-    void Init(const arma::mat& dataset, size_t start, size_t count) { }
+    template<typename MatType>
+    EmptyStatistic(const MatType& dataset,
+                   const size_t begin,
+                   const size_t count)
+    { }
 
     /**
-     * Initializes by combining statistics of two partitions.
-     *
+     * This constructor is called when a non-leaf node is created.
      * This lets you build fast bottom-up statistics when building trees.
+     *
+     * @param dataset Matrix that the tree is being built on.
+     * @param begin Starting index corresponding to this leaf.
+     * @param count Number of points held in this leaf.
+     * @param leftStat EmptyStatistic object of the left child node.
+     * @param rightStat EmptyStatistic object of the right child node.
      */
-    void Init(const arma::mat& dataset, size_t start, size_t count,
-        const EmptyStatistic& left_stat, const EmptyStatistic& right_stat) { }
+    template<typename MatType>
+    EmptyStatistic(const MatType& dataset,
+                   const size_t start,
+                   const size_t count,
+                   const EmptyStatistic& leftStat,
+                   const EmptyStatistic& rightStat)
+    { }
 };
 
 }; // namespace tree