private KdTreeNode <TValue> Build(TValue[] elementsArray, int startIndex, int endIndex, int depth)
{
var length = endIndex - startIndex + 1;
if (length == 0)
{
return(null);
}
// Sort array of elements by component of chosen dimension, in ascending magnitude.
_valueComparer.Dimension = depth % _nrOfDimensions;
Array.Sort(elementsArray, startIndex, length, _valueComparer);
// Select median element as pivot.
var medianIndex = startIndex + length / 2;
var medianElement = elementsArray[medianIndex];
// Create node and construct sub-trees around pivot element.
var node = new KdTreeNode <TValue>(medianElement);
node.LeftChild = Build(elementsArray, startIndex, medianIndex - 1, depth + 1);
node.RightChild = Build(elementsArray, medianIndex + 1, endIndex, depth + 1);
return(node);
}
public KdTree(IEnumerable <TValue> elements, params Func <TValue, double>[] valueSelectors)
{
_nrOfDimensions = valueSelectors.Length;
_valueSelectors = valueSelectors;
_valueComparer = new ValueLocationComparer(_valueSelectors);
var elementsArray = elements.ToArray();
_root = Build(elementsArray, 0, elementsArray.Length - 1, 0);
}
private void FindInRange(KdTreeNode <TValue> node, Vector location, double range, IList <TValue> valuesList, int depth)
{
if (node == null)
{
return;
}
var dimension = depth % _nrOfDimensions;
var nodeLocation = CreateVector(node.Value);
var distance = (nodeLocation - location).Abs();
// add to list if its in range
if (distance < range)
{
valuesList.Add(node.Value);
}
var nearChildNode = location[dimension] < nodeLocation[dimension] ? node.LeftChild : node.RightChild;
if (nearChildNode != null)
{
FindInRange(nearChildNode, location, range, valuesList, depth + 1);
}
// also other half needs to be checked?
if (range > Math.Abs(nodeLocation[dimension] - location[dimension]))
{
// Check for nodes in sub-tree of far child.
var farChildNode = nearChildNode == node.LeftChild ? node.RightChild : node.LeftChild;
if (farChildNode != null)
{
FindInRange(farChildNode, location, range, valuesList, depth + 1);
}
}
}