VptreeParam: The VptreeParam class
In LTLA/BiocNeighbors: Nearest Neighbor Detection for Bioconductor Packages

VptreeParam

R Documentation

The VptreeParam class

Description

A class to hold parameters for the vantage point (VP) tree algorithm for exact nearest neighbor identification.

Usage

VptreeParam(distance = c("Euclidean", "Manhattan", "Cosine"))

## S4 method for signature 'VptreeParam'
defineBuilder(BNPARAM)

Arguments

`distance`	String specifying the distance metric to use. Cosine distances are implemented as Euclidean distances on L2-normalized coordinates.
`BNPARAM`	A VptreeParam instance.

Details

In a VP tree (Yianilos, 1993), each node contains a subset of points that is split into two further partitions. The split is determined by picking an arbitrary point inside that subset as the node center, computing the distance to all other points from the center, and taking the median as the “radius”. The left child of this node contains all points within the median distance from the radius, while the right child contains the remaining points. This is applied recursively until all points resolve to individual nodes. The nearest neighbor search traverses the tree and exploits the triangle inequality between query points, node centers and thresholds to narrow the search space.

VP trees are often faster than more conventional KD-trees or ball trees as the former uses the points themselves as the nodes of the tree, avoiding the need to create many intermediate nodes and reducing the total number of distance calculations. Like KMKNN, it is also trivially extended to find all neighbors within a threshold distance from a query point.

Value

The VptreeParam constructor returns an instance of the VptreeParam class.

The defineBuilder method returns an external pointer that can be used in buildIndex to construct a VP tree index.

Author(s)

Aaron Lun

References

Yianilos PN (1993). Data structures and algorithms for nearest neighbor search in general metric spaces. Proceedings of the Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, 311-321.