# pairdist.default

##### Pairwise distances

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

##### Usage

```
# S3 method for default
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`

.

##### See Also

##### Examples

```
# NOT RUN {
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)
# }
```

*Documentation reproduced from package spatstat, version 1.60-1, License: GPL (>= 2)*