# nnwhich.pp3

0th

Percentile

##### Nearest neighbours in three dimensions

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

Keywords
spatial, math
##### Usage
## S3 method for class 'pp3':
nnwhich(X, \dots, k=1)
##### Arguments
X
Three-dimensional point pattern (object of class "pp3").
...
Ignored.
k
Integer, or integer vector. The algorithm will compute the distance to the kth nearest neighbour.
##### Details

For each point in the given three-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 "pp3".

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.

##### 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.

nnwhich, nndist, nncross

• nnwhich.pp3
##### Examples
X <- runifpoint3(30)
m <- nnwhich(X)
m2 <- nnwhich(X, k=2)
Documentation reproduced from package spatstat, version 1.31-3, License: GPL (>= 2)

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