nnwhich.pp3
Nearest neighbours in three dimensions
Finds the nearest neighbour of each point in a three-dimensional point pattern.
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 vectorvgiving the indices of the nearest neighbours (the nearest neighbout of theith point is thejth point wherej = v[i]). Ifkis a single integer, then the return value is a numeric vector giving the indices of thekth nearest neighbours.If
kis a vector, then the return value is a matrixmsuch thatm[i,j]is the index of thek[j]th nearest neighbour for theith data point.
Warnings
A value of NA is returned if there is only one point
in the point pattern.
See Also
Examples
X <- runifpoint3(30)
m <- nnwhich(X)
m2 <- nnwhich(X, k=2)