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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchlib.rankingexpression.evaluation.gbdtoptimization;
import com.yahoo.searchlib.rankingexpression.RankingExpression;
import com.yahoo.searchlib.rankingexpression.evaluation.ContextIndex;
import com.yahoo.searchlib.rankingexpression.evaluation.OptimizationReport;
import com.yahoo.searchlib.rankingexpression.evaluation.Optimizer;
import com.yahoo.searchlib.rankingexpression.rule.ArithmeticNode;
import com.yahoo.searchlib.rankingexpression.rule.ArithmeticOperator;
import com.yahoo.searchlib.rankingexpression.rule.CompositeNode;
import com.yahoo.searchlib.rankingexpression.rule.ExpressionNode;
import java.util.ArrayList;
import java.util.List;
/**
* @author bratseth
*/
public class GBDTForestOptimizer extends Optimizer {
private OptimizationReport report;
/**
* A temporary value used within the algorithm
*/
private int currentTreesOptimized = 0;
/**
* Optimizes sums of GBDTNodes by replacing them by a single GBDTForestNode
*
* @param expression the expression to destructively optimize
* @param context a fast lookup context created from the given expression
* @param report the optimization report to which actions of this is logged
*/
@Override
public void optimize(RankingExpression expression, ContextIndex context, OptimizationReport report) {
if ( ! isEnabled()) return;
this.report = report;
expression.setRoot(findAndOptimize(expression.getRoot()));
report.note("GBDT forest optimization done");
}
/**
* Recursively descend and optimize gbdt forest nodes.
*
* @return the resulting node, which may be the input node if no optimizations were found
*/
private ExpressionNode findAndOptimize(ExpressionNode node) {
ExpressionNode newNode = optimize(node);
if ( ! (newNode instanceof CompositeNode)) return newNode; //
CompositeNode newComposite = (CompositeNode)newNode;
List<ExpressionNode> newChildren = new ArrayList<>();
for (ExpressionNode child : newComposite.children()) {
newChildren.add(findAndOptimize(child));
}
return newComposite.setChildren(newChildren);
}
/**
* Optimize the given node (only)
*
* @return the resulting node, which may be the input node if it could not be optimized
*/
private ExpressionNode optimize(ExpressionNode node) {
currentTreesOptimized = 0;
List<Double> forest = new ArrayList<>();
boolean optimized = optimize(node, forest);
if ( ! optimized ) return node;
GBDTForestNode forestNode = new GBDTForestNode(toArray(forest));
report.incMetric("Number of forests", 1);
report.incMetric("GBDT trees optimized to forests", currentTreesOptimized);
return forestNode;
}
/**
* Optimize the given node, if it is the root of a gdbt forest. Otherwise do nothing and return false
*/
private boolean optimize(ExpressionNode node, List<Double> forest) {
if (node instanceof GBDTNode) {
addTo(forest, (GBDTNode)node);
currentTreesOptimized++;
return true;
}
if (!(node instanceof ArithmeticNode)) {
return false;
}
ArithmeticNode aNode = (ArithmeticNode)node;
for (ArithmeticOperator op : aNode.operators()) {
if (op != ArithmeticOperator.PLUS) {
return false;
}
}
for (ExpressionNode child : aNode.children()) {
if (!optimize(child, forest)) {
return false;
}
}
return true;
}
private void addTo(List<Double> forest, GBDTNode tree) {
forest.add((double)tree.values().length);
addAll(tree.values(), forest);
}
private void addAll(double[] values, List<Double> forest) {
for (double value : values) {
forest.add(value);
}
}
private double[] toArray(List<Double> valueList) {
double[] valueArray = new double[valueList.size()];
for (int i = 0; i < valueList.size(); i++) {
valueArray[i] = valueList.get(i);
}
return valueArray;
}
}
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