nnspat (version 0.1.2)

NN: Finding the index of the NN of a given point

Description

Returns the index (or indices) of the nearest neighbor(s) of subject \(i\) given data set or IPD matrix x. It will yield a vector if there are ties, and subject indices correspond to rows (i.e., rows 1:n ) if x is the data set and to rows or columns if x is the IPD matrix.

The argument is.ipd is a logical argument (default=TRUE) to determine the structure of the argument x. If TRUE, x is taken to be the inter-point distance (IPD) matrix, and if FALSE, x is taken to be the data set with rows representing the data points.

Usage

NN(x, i, is.ipd = TRUE, ...)

Value

Returns the index (indices) i.e., row number(s) of the NN of subject \(i\)

Arguments

x

The IPD matrix (if is.ipd=TRUE) or a data set of points in matrix or data frame form where points correspond to the rows (if is.ipd = FALSE).

i

index of (i.e., row number for) the subject whose NN is to be found.

is.ipd

A logical parameter (default=TRUE). If TRUE, x is taken as the inter-point distance matrix, otherwise, x is taken as the data set with rows representing the data points.

...

are for further arguments, such as method and p, passed to the dist function.

Author

Elvan Ceyhan

See Also

kNN and NNsub

Examples

#3D data points
n<-20  #or try sample(1:20,1)
Y<-matrix(runif(3*n),ncol=3)
ipd<-ipd.mat(Y)
NN(ipd,1)
NN(Y,1,is.ipd = FALSE)
NN(ipd,5)
NN(Y,5,is.ipd = FALSE)
NN(Y,5,is.ipd = FALSE,method="max")

#1D data points
X<-as.matrix(runif(15)) # need to be entered as a matrix with one column
#(i.e., a column vector), hence X<-runif(5) would not work
ipd<-ipd.mat(X)
NN(ipd,1)
NN(ipd,5)

#with possible ties in the data
Y<-matrix(round(runif(30)*10),ncol=3)
ny<-nrow(Y)
ipd<-ipd.mat(Y)
for (i in 1:ny)
  cat(i,":",NN(ipd,i),"|",NN(Y,i,is.ipd = FALSE),"\n")