spatstat (version 1.23-1)

nnwhich.ppx: Nearest Neighbours in Any Dimensions

Description

Finds the nearest neighbour of each point in a multi-dimensional point pattern.

Usage

## S3 method for class 'ppx':
nnwhich(X, \dots, k=1)

Arguments

X

Multi-dimensional point pattern (object of class "ppx").

...

Arguments passed to coords.ppx to determine which coordinates should be used.

k

Integer, or integer vector. The algorithm will compute the distance to the kth nearest neighbour.

Value

• Numeric vector or matrix giving, for each point, the index of its nearest neighbour (or kth nearest neighbour).

  If k = 1 (the default), the return value is a numeric vector v giving the indices of the nearest neighbours (the nearest neighbout of the ith point is the jth point where j = v[i]). If k is a single integer, then the return value is a numeric vector giving the indices of the kth nearest neighbours.

  If k is a vector, then the return value is a matrix m such that m[i,j] is the index of the k[j]th nearest neighbour for the ith data point.

Warnings

A value of NA is returned if there is only one point in the point pattern.

Details

For each point in the given multi-dimensional point pattern, this function finds its nearest neighbour (the nearest other point of the pattern). By default it returns a vector giving, for each point, the index of the point's nearest neighbour. If k is specified, the algorithm finds each point's kth nearest neighbour.

The function nnwhich is generic. This is the method for the class "ppx".

If there are no points in the pattern, a numeric vector of length zero is returned. If there is only one point, then the nearest neighbour is undefined, and a value of NA is returned. In general if the number of points is less than or equal to k, then a vector of NA's is returned.

To evaluate the distance between a point and its nearest neighbour, use nndist.

To find the nearest neighbours from one point pattern to another point pattern, use nncross. By default, both spatial and temporal coordinates are extracted. To obtain the spatial distance between points in a space-time point pattern, set temporal=FALSE.

See Also

nnwhich, nndist, nncross

Examples

df <- data.frame(x=runif(5),y=runif(5),z=runif(5),w=runif(5))
   X <- ppx(data=df)
   m <- nnwhich(X)
   m2 <- nnwhich(X, k=2)