/// <summary>
/// Post-order tree traversal method.
/// </summary>
///
/// <remarks>
/// Adapted from John Cowan (1998) recommendation.
/// </remarks>
///
public static IEnumerator <DecisionNode> PostOrder(DecisionNode tree)
{
var cursor = new Dictionary <DecisionNode, int>();
DecisionNode currentNode = tree;
while (currentNode != null)
{
// Move down to first child
DecisionNode nextNode = null;
if (currentNode.Branches != null)
{
nextNode = currentNode.Branches.FirstOrDefault();
}
if (nextNode != null)
{
currentNode = nextNode;
continue;
}
// No child nodes, so walk tree
while (currentNode != null)
{
yield return(currentNode); // post order
// Move to sibling if possible.
nextNode = GetNextSibling(cursor, currentNode);
if (nextNode != null)
{
currentNode = nextNode;
break;
}
// Move up
if (currentNode == nextNode)
{
currentNode = null;
}
else
{
currentNode = currentNode.Parent;
}
}
}
}
private void create(DecisionNode node, int depth)
{
string indent = new string(' ', depth * 4);
if (!node.IsLeaf)
{
int attributeIndex = node.Branches.AttributeIndex;
// Create all comparison expressions
for (int i = 0; i < node.Branches.Count; i++)
{
DecisionNode child = node.Branches[i];
string cmp = ComparisonExtensions.ToString(child.Comparison);
if (i == 0)
{
writer.Write(indent + "if ");
}
else
{
writer.Write(indent + "else if ");
}
writer.Write("(input[{0}] {1} {2}) {{", attributeIndex, cmp, child.Value);
writer.WriteLine();
create(child, depth + 1);
writer.WriteLine(indent + "}");
}
writer.WriteLine(indent + "else throw new ArgumentException(\"input\", \"Unexpected value at position " + attributeIndex + ".\");");
}
else // node is a leaf
{
if (node.Output.HasValue)
{
writer.WriteLine(indent + "return " + node.Output.Value + ";");
}
else
{
writer.WriteLine(indent + "return -1;");
}
}
}
/// <summary>
/// Depth-first traversal method.
/// </summary>
///
public static IEnumerator <DecisionNode> DepthFirst(DecisionNode tree)
{
if (tree == null)
{
yield break;
}
var stack = new Stack <DecisionNode>(new[] { tree });
while (stack.Count != 0)
{
DecisionNode current = stack.Pop();
yield return(current);
if (current.Branches != null)
{
for (int i = current.Branches.Count - 1; i >= 0; i--)
{
stack.Push(current.Branches[i]);
}
}
}
}
/// <summary>
/// Breadth-first traversal method.
/// </summary>
///
public static IEnumerator <DecisionNode> BreadthFirst(DecisionNode tree)
{
if (tree == null)
{
yield break;
}
var queue = new Queue <DecisionNode>(new[] { tree });
while (queue.Count != 0)
{
DecisionNode current = queue.Dequeue();
yield return(current);
if (current.Branches != null)
{
foreach (var child in current.Branches)
{
queue.Enqueue(child);
}
}
}
}
internal static DecisionNode GetNextSibling(Dictionary <DecisionNode, int> cursors, DecisionNode node)
{
var parent = node.Parent;
if (parent == null)
{
return(null);
}
// Get current node index
int index;
if (!cursors.TryGetValue(node, out index))
{
cursors[node] = index = 0;
}
int nextIndex = index + 1;
if (nextIndex < parent.Branches.Count)
{
var sibling = parent.Branches[nextIndex];
cursors[sibling] = nextIndex;
return(sibling);
}
return(null);
}
private Expression create(DecisionNode node)
{
if (!node.IsLeaf)
{
int attributeIndex = node.Branches.AttributeIndex;
// Create all comparison expressions
BinaryExpression[] comparisons = new BinaryExpression[node.Branches.Count];
Expression[] childExpression = new Expression[node.Branches.Count];
for (int i = 0; i < comparisons.Length; i++)
{
DecisionNode child = node.Branches[i];
var expr = Expression.ArrayIndex(inputs, Expression.Constant(attributeIndex));
var cons = Expression.Constant(child.Value);
switch (child.Comparison)
{
case ComparisonKind.Equal:
comparisons[i] = Expression.Equal(expr, cons); break;
case ComparisonKind.GreaterThan:
comparisons[i] = Expression.GreaterThan(expr, cons); break;
case ComparisonKind.GreaterThanOrEqual:
comparisons[i] = Expression.GreaterThanOrEqual(expr, cons); break;
case ComparisonKind.LessThan:
comparisons[i] = Expression.LessThan(expr, cons); break;
case ComparisonKind.LessThanOrEqual:
comparisons[i] = Expression.LessThanOrEqual(expr, cons); break;
case ComparisonKind.NotEqual:
comparisons[i] = Expression.NotEqual(expr, cons); break;
default:
throw new InvalidOperationException("Unexpected node comparison type.");
}
childExpression[i] = create(node.Branches[i]);
}
// Create expression for else expressions
ConstructorInfo ex = typeof(ArgumentException).GetConstructor(new[] { typeof(string), typeof(string) });
var lastElse = Expression.IfThenElse(comparisons[comparisons.Length - 1],
childExpression[comparisons.Length - 1],
Expression.Throw(Expression.New(ex,
Expression.Constant("Input contains a value outside of expected ranges."),
Expression.Constant("input"))));
ConditionalExpression currentIf = null;
for (int i = comparisons.Length - 2; i >= 0; i--)
{
currentIf = Expression.IfThenElse(comparisons[i],
childExpression[i], lastElse);
lastElse = currentIf;
}
return(currentIf);
}
else // node is a leaf
{
if (node.Output.HasValue)
{
return(Expression.Return(label, Expression.Constant(node.Output.Value), typeof(int)));
}
return(Expression.Return(label, Expression.Constant(-1), typeof(int)));
}
}
