smacpod (version 2.6)

nn: Determine nearest neighbors

Description

nn determines the nearest neighbors for a set of observations based on a distance matrix.

Usage

nn(d, k, method = "c", self = FALSE)

Value

Returns a list with the nearest neighbors of each observation. For each element of the list, the indices order neighbors from nearest to farthest.

Arguments

d

A square distance matrix for the coordinates of interest.

k

The number of neighbors to return (if method = "c") or the distance for which observations are considered neighbors (if method = "d").

method

The method of determining the neighbors. The default is "c", specifying that the k nearest neighbors (the number of neighbors) for each observation should be returned. The alternative is "d", meaning that neighbors are determined by their distance from an observation. In that case, two observations are neighbors if their separation distance is less or equal to k.

self

A logical indicating whether an observation is a neighbor with itself. The default is FALSE.

Author

Joshua French

Details

This function determine nearest neighbors in two ways: 1. number of neighbors or 2. distance.

If method = "c", then k specifies the total number of neighbors to return for each observation.

If method = "d", then k specifies the maximum distance for which an observation is considered a neighbor.

The function returns the neighbors for each observation.

Examples

data(grave)
# make distance matrix
d = as.matrix(dist(cbind(grave$x, grave$y)))
# 3 nearest neighbors
nnc = nn(d, k = 3, method = "c")
# nearest neighbors within k units of each observation
nnd = nn(d, k = 200, method = "d")