smile.base.cart.Split Maven / Gradle / Ivy
/*
* Copyright (c) 2010-2021 Haifeng Li. All rights reserved.
*
* Smile is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Smile is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Smile. If not, see comparator = Comparator.comparingDouble(x -> x.score);
/** The node associated with this split. */
final LeafNode leaf;
/**
* The split feature for this node.
*/
final int feature;
/**
* Reduction in splitting criterion.
*/
final double score;
/**
* The inclusive lower bound of the data partition in the reordered sample index array.
*/
final int lo;
/**
* The exclusive upper bound of the data partition in the reordered sample index array.
*/
final int hi;
/** The number of samples in true branch. */
final int trueCount;
/** The number of samples in false branch. */
final int falseCount;
/** The parent node of the leaf to be split. */
InternalNode parent;
/**
* unsplittable[j] is true if
*
* - The column j in the node is constant
* - The column j is almost constant, i.e. but after the split,
* the size of one or two children is less than nodeSize.
* - The column j is not (almost) constant, but the impurity of
* node doesn't decrease after the split. Therefore, the mutual
* information between y and column j is very low.
*
* For the first two cases, the column j in the children nodes
* (split on another column) are still unsplittable. In last case,
* column j may become splittable later after the node splits on
* another column. However, we still would like to ignore it
* because of the low mutual information. It likely introduces
* more noise than information.
*/
boolean[] unsplittable;
/** The depth of node in the tree. */
int depth = 1;
/**
* Constructor.
* @param leaf the node to split.
* @param feature the index of feature column.
* @param score the split score.
* @param lo the lower bound of sample index in the node.
* @param hi the upper bound of sample index in the node.
* @param trueCount the number of samples in true branch child.
* @param falseCount the number of samples false branch child.
*/
public Split(LeafNode leaf, int feature, double score, int lo, int hi, int trueCount, int falseCount) {
this.leaf = leaf;
this.feature = feature;
this.score = score;
this.lo = lo;
this.hi = hi;
this.trueCount = trueCount;
this.falseCount = falseCount;
}
/**
* Returns an internal node with the feature, value, and score of this split.
* @param trueChild the child node of true branch.
* @param falseChild the child node of false branch.
* @return an internal node
*/
public abstract InternalNode toNode(Node trueChild, Node falseChild);
/**
* Returns the lambda that tests on the split feature.
* @return the lambda that tests on the split feature.
*/
public abstract IntPredicate predicate();
@Override
public String toString() {
String[] fields = {
"feature: " + feature,
"score: " + score,
"lo: " + lo,
"hi: " + hi,
"true: " + trueCount,
"false: " + falseCount,
"depth: " + depth
};
return Arrays.stream(fields).collect(Collectors.joining(",\n", "{\n", "\n}"));
}
}