dbscan (version 1.1-8)

kNNdist: Calculate and Plot k-Nearest Neighbor Distances

Description

Fast calculation of the k-nearest neighbor distances for a dataset represented as a matrix of points. The kNN distance is defined as the distance from a point to its k nearest neighbor. The kNN distance plot displays the kNN distance of all points sorted from smallest to largest. The plot can be used to help find suitable parameter values for the for DBSCAN.

Usage

kNNdist(x, k, all = FALSE, ...)
kNNdistplot(x, k, ...)

Arguments

x

the data set as a matrix of points (Euclidean distance is used) or a precalculated dist object.

k

number of nearest neighbors used for the distance calculation.

all

should a matrix with the distances to all k nearest neighbors be returned?

...

further arguments (e.g., kd-tree related parameters) are passed on to kNN.

Value

kNNdist returns a numeric vector with the distance to its k nearest neighbor. If all = TRUE then a matrix with k columns containing the distances to all 1st, 2nd, ..., kth nearest neighbors is returned instead.

See Also

kNN.

Examples

# NOT RUN {
data(iris)
iris <- as.matrix(iris[,1:4])

## Find the 4-NN distance for each observation (see ?kNN
## for different search strategies)
kNNdist(iris, k = 4)

## Get a matrix with distances to the 1st, 2nd, ..., 4th NN.
kNNdist(iris, k = 4, all = TRUE)

## Produce a k-NN distance plot to determine a suitable eps for
## DBSCAN with MinPts = 5. Use k = 4 (= MinPts -1).
## The knee is visible around a distance of .7
kNNdistplot(iris, k = 4)

cl <- dbscan(iris, eps = .7, minPts = 5)
pairs(iris, col = cl$cluster+1L)
## Note: black points are noise points
# }