closepaircounts | R Documentation |

Low-level functions to count the number of close pairs of points.

closepaircounts(X, r) crosspaircounts(X, Y, r)

`X,Y` |
Point patterns (objects of class |

`r` |
Maximum distance between pairs of points to be counted as close pairs. |

These are the efficient low-level functions used by spatstat to count close pairs of points in a point pattern or between two point patterns.

`closepaircounts(X,r)`

counts the number of neighbours for
each point in the pattern `X`

. That is, for each point
`X[i]`

, it counts the number of other points `X[j]`

with `j != i`

such that `d(X[i],X[j]) <= r`

where
`d`

denotes Euclidean distance. The result is an integer vector
`v`

such that `v[i]`

is the number of neighbours of
`X[i]`

.

`crosspaircounts(X,Y,r)`

counts, for each point
in the pattern `X`

, the number of neighbours in the pattern
`Y`

. That is, for each point
`X[i]`

, it counts the number of points `Y[j]`

such that `d(X[i],X[j]) <= r`

. The result is an integer vector
`v`

such that `v[i]`

is the number of neighbours of
`X[i]`

in the pattern `Y`

.

An integer vector of length equal to the number of points in `X`

.

The results of these functions may not agree exactly with
the correct answer (as calculated by a human) and may not
be consistent between different computers and different installations
of **R**. The discrepancies arise in marginal cases where the interpoint
distance is equal to, or very close to, the threshold `rmax`

.

Floating-point numbers in a computer
are not mathematical Real Numbers: they are approximations using
finite-precision binary arithmetic.
The approximation is accurate to a tolerance of about
`.Machine$double.eps`

.

If the true interpoint distance *d* and the threshold `rmax`

are equal, or if their difference is no more than `.Machine$double.eps`

,
the result may be incorrect.

and \rolf

`closepairs`

to identify all close pairs of points.

a <- closepaircounts(cells, 0.1) sum(a) Y <- split(amacrine) b <- crosspaircounts(Y$on, Y$off, 0.1)

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