Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/2125#discussion_r16696040
--- Diff: mllib/src/main/scala/org/apache/spark/mllib/tree/model/Node.scala
---
@@ -148,3 +145,50 @@ class Node (
}
}
+
+private[tree] object Node {
+
+ /**
+ * Return the index of the left child of this node.
+ */
+ def leftChildIndex(nodeIndex: Int): Int = nodeIndex * 2
+
+ /**
+ * Return the index of the right child of this node.
+ */
+ def rightChildIndex(nodeIndex: Int): Int = nodeIndex * 2 + 1
+
+ /**
+ * Get the parent index of the given node, or 0 if it is the root.
+ */
+ def parentIndex(nodeIndex: Int): Int = nodeIndex >> 1
+
+ /**
+ * Return the level of a tree which the given node is in.
+ */
+ def indexToLevel(nodeIndex: Int): Int = if (nodeIndex == 0) {
+ throw new IllegalArgumentException(s"0 is not a valid node index.")
+ } else {
+
java.lang.Integer.numberOfTrailingZeros(java.lang.Integer.highestOneBit(nodeIndex))
+ }
+
+ /**
+ * Returns true if this is a left child.
+ * Note: Returns false for the root.
+ */
+ def isLeftChild(nodeIndex: Int): Boolean = nodeIndex > 1 && nodeIndex %
2 == 0
+
+ /**
+ * Return the maximum number of nodes which can be in the given level of
the tree.
+ * @param level Level of tree (0 = root).
+ */
+ private[tree] def maxNodesInLevel(level: Int): Int = 1 << level
+
+ /**
+ * Return the maximum number of nodes which can be in or above the given
level of the tree
+ * (i.e., for the entire subtree from the root to this level).
+ * @param level Level of tree (0 = root).
+ */
+ private[tree] def maxNodesInSubtree(level: Int): Int = (1 << level + 1)
- 1
--- End diff --
This is mostly used in determining the starting node index of a level.
Shall we add a new method called `startIndexInLevel(level: Int): Int = 1 <<
level`? Also the name `subtree` is usually used to refer the entire descendants
of a node.
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