/** Implementation of the FindBestSplit algorithm from E.Ikonomovska et al. */
protected AttributeSplitSuggestion searchForBestSplitOption(
Node currentNode,
AttributeSplitSuggestion currentBestOption,
SplitCriterion criterion,
int attIndex) {
// Return null if the current node is null or we have finished looking through all the possible
// splits
if (currentNode == null || rightTotal == 0.0) {
return currentBestOption;
}
if (currentNode.left != null) {
currentBestOption =
searchForBestSplitOption(currentNode.left, currentBestOption, criterion, attIndex);
}
sumTotalLeft += currentNode.leftStatistics.getValue(1);
sumTotalRight -= currentNode.leftStatistics.getValue(1);
sumSqTotalLeft += currentNode.leftStatistics.getValue(2);
sumSqTotalRight -= currentNode.leftStatistics.getValue(2);
rightTotal -= currentNode.leftStatistics.getValue(0);
double[][] postSplitDists =
new double[][] {
{currentNode.leftStatistics.getValue(0), sumTotalLeft, sumSqTotalLeft},
{rightTotal, sumTotalRight, sumSqTotalRight}
};
double[] preSplitDist =
new double[] {
(currentNode.leftStatistics.getValue(0) + rightTotal),
(sumTotalLeft + sumTotalRight),
(sumSqTotalLeft + sumSqTotalRight)
};
double merit = criterion.getMeritOfSplit(preSplitDist, postSplitDists);
if ((currentBestOption == null) || (merit > currentBestOption.merit)) {
currentBestOption =
new AttributeSplitSuggestion(
new NumericAttributeBinaryTest(attIndex, currentNode.cut_point, true),
postSplitDists,
merit);
}
if (currentNode.right != null) {
currentBestOption =
searchForBestSplitOption(currentNode.right, currentBestOption, criterion, attIndex);
}
sumTotalLeft -= currentNode.leftStatistics.getValue(1);
sumTotalRight += currentNode.leftStatistics.getValue(1);
sumSqTotalLeft -= currentNode.leftStatistics.getValue(2);
sumSqTotalRight += currentNode.leftStatistics.getValue(2);
rightTotal += currentNode.leftStatistics.getValue(0);
return currentBestOption;
}
/**
* Recursive method that first checks all of a node's children before deciding if it is 'bad' and
* may be removed
*/
private boolean removeBadSplitNodes(
SplitCriterion criterion,
Node currentNode,
double lastCheckRatio,
double lastCheckSDR,
double lastCheckE) {
boolean isBad = false;
if (currentNode == null) {
return true;
}
if (currentNode.left != null) {
isBad =
removeBadSplitNodes(
criterion, currentNode.left, lastCheckRatio, lastCheckSDR, lastCheckE);
}
if (currentNode.right != null && isBad) {
isBad =
removeBadSplitNodes(
criterion, currentNode.left, lastCheckRatio, lastCheckSDR, lastCheckE);
}
if (isBad) {
double[][] postSplitDists =
new double[][] {
{
currentNode.leftStatistics.getValue(0),
currentNode.leftStatistics.getValue(1),
currentNode.leftStatistics.getValue(2)
},
{
currentNode.rightStatistics.getValue(0),
currentNode.rightStatistics.getValue(1),
currentNode.rightStatistics.getValue(2)
}
};
double[] preSplitDist =
new double[] {
(currentNode.leftStatistics.getValue(0) + currentNode.rightStatistics.getValue(0)),
(currentNode.leftStatistics.getValue(1) + currentNode.rightStatistics.getValue(1)),
(currentNode.leftStatistics.getValue(2) + currentNode.rightStatistics.getValue(2))
};
double merit = criterion.getMeritOfSplit(preSplitDist, postSplitDists);
if ((merit / lastCheckSDR) < (lastCheckRatio - (2 * lastCheckE))) {
currentNode = null;
return true;
}
}
return false;
}
