private static KdTreeNode <TValue> Construct(KdTree <TValue, TField> tree, TValue[] elements, int startIndex,
int endIndex, int depth, ValueLocationComparer valueLocationComparer)
{
var length = endIndex - startIndex + 1;
if (length == 0)
{
return(null);
}
// Sort array of elements by component of chosen dimension, in ascending magnitude.
valueLocationComparer.Dimension = depth % tree.dimensionality;
Array.Sort(elements, startIndex, length, valueLocationComparer);
// Select median element as pivot.
var medianIndex = startIndex + length / 2;
var medianElement = elements[medianIndex];
// Create node and construct sub-trees around pivot element.
var node = new KdTreeNode <TValue>(medianElement);
node.LeftChild = Construct(tree, elements, startIndex, medianIndex - 1, depth + 1, valueLocationComparer);
node.RightChild = Construct(tree, elements, medianIndex + 1, endIndex, depth + 1, valueLocationComparer);
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);
}
