pairdist.default: Pairwise distances

In spatstat.geom: Geometrical Functionality of the 'spatstat' Family

Pairwise distances

Description

Computes the matrix of distances between all pairs of points in a set of points in two dimensional space

Usage

  ## Default S3 method:
pairdist(X, Y=NULL, ..., period=NULL, method="C", squared=FALSE)

Arguments

X, Y	Arguments specifying the coordinates of a set of points. Typically X and Y would be numeric vectors of equal length. Alternatively Y may be omitted and X may be a list with two components x and y, or a matrix with two columns.
...	Ignored.
period	Optional. Dimensions for periodic edge correction.
method	String specifying which method of calculation to use. Values are "C" and "interpreted". Usually not specified.
squared	Logical. If squared=TRUE, the squared distances are returned instead (this computation is faster).

Details

Given the coordinates of a set of points in two dimensional space, this function computes the Euclidean distances between all pairs of points, and returns the matrix of distances. It is a method for the generic function pairdist.

Note: If only pairwise distances within some threshold value are needed the low-level function closepairs may be much faster to use.

The arguments X and Y must determine the coordinates of a set of points. Typically X and Y would be numeric vectors of equal length. Alternatively Y may be omitted and X may be a list with two components named x and y, or a matrix or data frame with two columns.

For typical input the result is numerically equivalent to (but computationally faster than) as.matrix(dist(x)) where x = cbind(X, Y), but that command is useful for calculating all pairwise distances between points in k-dimensional space when x has k columns.

Alternatively if period is given, then the distances will be computed in the ‘periodic’ sense (also known as ‘torus’ distance). The points will be treated as if they are in a rectangle of width period[1] and height period[2]. Opposite edges of the rectangle are regarded as equivalent.

If squared=TRUE then the squared Euclidean distances d^2 are returned, instead of the Euclidean distances d. The squared distances are faster to calculate, and are sufficient for many purposes (such as finding the nearest neighbour of a point).

The argument method is not normally used. It is retained only for checking the validity of the software. If method = "interpreted" then the distances are computed using interpreted R code only. If method="C" (the default) then C code is used. The C code is somewhat faster.

Value

A square matrix whose [i,j] entry is the distance between the points numbered i and j.

Author(s)

\pavel

and \adrian.

See Also

crossdist, nndist, Kest, closepairs

Examples

   x <- runif(100)
   y <- runif(100)
   d <- pairdist(x, y)
   d <- pairdist(cbind(x,y))
   d <- pairdist(x, y, period=c(1,1))
   d <- pairdist(x, y, squared=TRUE)

spatstat.geom documentation built on Sept. 18, 2024, 9:08 a.m.