private static void AppendLeaves(IDataNode node, List <DataLeaf> leaves)
{
if (node is DataLeaf)
{
leaves.Add((DataLeaf)node);
}
else if (node is IDataSplit)
{
IDataSplit split = (IDataSplit)node;
AppendLeaves(split.Left, leaves);
AppendLeaves(split.Right, leaves);
}
else
{
throw new ArgumentException("Unknown node type: " + node);
}
}
private DataNodeAccuracy PruneDecisionTree(IDataNode node)
{
if (node is DataLeaf)
{
return(new DataNodeAccuracy {
Node = node,
CorrectWeight = node.ClassDistribution.Max(),
TotalWeight = node.ClassDistribution.Sum(),
});
}
else if (node is IDataSplit)
{
IDataSplit split = (IDataSplit)node;
DataNodeAccuracy leftAccuracy = PruneDecisionTree(split.Left);
DataNodeAccuracy rightAccuracy = PruneDecisionTree(split.Right);
float splitCorrect = leftAccuracy.CorrectWeight + rightAccuracy.CorrectWeight;
float splitTotal = leftAccuracy.TotalWeight + rightAccuracy.TotalWeight;
float leafCorrect = node.ClassDistribution.Max();
float leafTotal = node.ClassDistribution.Sum();
#if DEBUGCUDA
Assert.AreEqual(leafTotal, splitTotal, 1.0f);
#endif
float accuracyIncrease = splitCorrect - leafCorrect;
float requiredIncrease = Context.TotalWeight * GPUConstants.RequiredImprovementToSplit;
if (accuracyIncrease < requiredIncrease)
{
// Split not justified, revert back to leaf at this level
return(new DataNodeAccuracy {
Node = new DataLeaf {
ClassDistribution = node.ClassDistribution
},
CorrectWeight = leafCorrect,
TotalWeight = leafTotal,
});
}
else
{
// Take the split with the pruned nodes
if (split is AttributeSplit)
{
AttributeSplit attributeSplit = (AttributeSplit)split;
attributeSplit.Left = leftAccuracy.Node;
attributeSplit.Right = rightAccuracy.Node;
}
else if (split is CategoricalSplit)
{
CategoricalSplit categoricalSplit = (CategoricalSplit)split;
categoricalSplit.Left = leftAccuracy.Node;
categoricalSplit.Right = rightAccuracy.Node;
}
else
{
throw new ArgumentException("Unknown split type: " + split);
}
return(new DataNodeAccuracy {
Node = split,
CorrectWeight = splitCorrect,
TotalWeight = splitTotal,
});
}
}
else
{
throw new ArgumentException("Unknown node type: " + node);
}
}