knearneigh
From spdep v0.69
by Roger Bivand
K nearest neighbours for spatial weights
The function returns a matrix with the indices of points belonging to the set of the k nearest neighbours of each other. If longlat = TRUE, Great Circle distances are used. A warning will be given if identical points are found.
 Keywords
 spatial
Usage
knearneigh(x, k=1, longlat = NULL, RANN=TRUE)
Arguments
 x
 matrix of point coordinates or a SpatialPoints object
 k
 number of nearest neighbours to be returned
 longlat
 TRUE if point coordinates are longitudelatitude decimal degrees, in which case distances are measured in kilometers; if x is a SpatialPoints object, the value is taken from the object itself
 RANN
 logical value, if the RANN package is available, use for finding k nearest neighbours when longlat is FALSE, and when there are no identical points
Details
The underlying C code is based on the knn
function in the class package.
Value

A list of class
knn
See Also
knn
, dnearneigh
,
knn2nb
, nn2
Examples
example(columbus)
coords < coordinates(columbus)
col.knn < knearneigh(coords, k=4)
plot(columbus, border="grey")
plot(knn2nb(col.knn), coords, add=TRUE)
title(main="K nearest neighbours, k = 4")
data(state)
us48.fipsno < read.geoda(system.file("etc/weights/us48.txt",
package="spdep")[1])
if (as.numeric(paste(version$major, version$minor, sep="")) < 19) {
m50.48 < match(us48.fipsno$"State.name", state.name)
} else {
m50.48 < match(us48.fipsno$"State_name", state.name)
}
xy < as.matrix(as.data.frame(state.center))[m50.48,]
llk4.nb < knn2nb(knearneigh(xy, k=4, longlat=FALSE))
gck4.nb < knn2nb(knearneigh(xy, k=4, longlat=TRUE))
plot(llk4.nb, xy)
plot(diffnb(llk4.nb, gck4.nb), xy, add=TRUE, col="red", lty=2)
title(main="Differences between Euclidean and Great Circle k=4 neighbours")
summary(llk4.nb, xy, longlat=TRUE)
summary(gck4.nb, xy, longlat=TRUE)
xy1 < SpatialPoints((as.data.frame(state.center))[m50.48,],
proj4string=CRS("+proj=longlat +ellps=GRS80"))
gck4a.nb < knn2nb(knearneigh(xy1, k=4))
summary(gck4a.nb, xy1)
Community examples
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