# Extract.ppx

##### Extract Subset of Multidimensional Point Pattern

Extract a subset of a multidimensional point pattern.

##### Usage

```
# S3 method for ppx
[(x, i, drop=FALSE, ...)
```

##### Arguments

- x
A multidimensional point pattern (object of class

`"ppx"`

).- i
Subset index. A valid subset index in the usual R sense, indicating which points should be retained; or a spatial domain of class

`"boxx"`

or`"box3"`

.- drop
Logical value indicating whether to remove unused levels of the marks, if the marks are a factor.

- …
Ignored.

##### Details

This function extracts a designated subset of a multidimensional point pattern.

The function `[.ppx`

is a method for `[`

for the
class `"ppx"`

. It extracts a designated subset of a point pattern.
The argument `i`

may be either

a subset index in the usual R sense: either a numeric vector of positive indices (identifying the points to be retained), a numeric vector of negative indices (identifying the points to be deleted) or a logical vector of length equal to the number of points in the point pattern

`x`

. In the latter case, the points`(x$x[i], x$y[i])`

for which`subset[i]=TRUE`

will be retained, and the others will be deleted.a spatial domain of class

`"boxx"`

or`"box3"`

. Points falling inside this region will be retained.

The argument `drop`

determines whether to remove
unused levels of a factor, if the point pattern is multitype
(i.e. the marks are a factor) or if the marks are a data frame or hyperframe
in which some of the columns are factors.

Use the function `unmark`

to remove marks from a
marked point pattern.

##### Value

A multidimensional point pattern (of class `"ppx"`

).

##### See Also

##### Examples

```
# NOT RUN {
df <- data.frame(x=runif(4),y=runif(4),z=runif(4))
X <- ppx(data=df, coord.type=c("s","s","t"))
X[-2]
# }
```

*Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)*