# Extract.lpp

##### Extract Subset of Point Pattern on Linear Network

Extract a subset of a point pattern on a linear network.

##### Usage

```
# S3 method for lpp
[(x, i, j, drop=FALSE, …, snip=TRUE)
```

##### Arguments

- x
A point pattern on a linear network (object of class

`"lpp"`

).- i
Subset index. A valid subset index in the usual R sense, indicating which points should be retained.

- j
Spatial window (object of class

`"owin"`

) delineating the region that should be retained.- drop
Logical value indicating whether to remove unused levels of the marks, if the marks are a factor.

- snip
Logical. If

`TRUE`

(the default), segments of the network which cross the boundary of the window`j`

will be cut by the boundary. If`FALSE`

, these segments will be deleted.- …
Ignored.

##### Details

This function extracts a designated subset of a point pattern on a linear network.

The function `[.lpp`

is a method for `[`

for the
class `"lpp"`

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

should be 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.

The argument `j`

, if present, should be a spatial window.
The pattern inside the region will be retained.
*Line segments that cross the boundary of the window
are deleted* in the current implementation.

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.

The argument `snip`

specifies what to do with segments of
the network which cross the boundary of the window `j`

.
If `snip=FALSE`

, such segments are simply deleted.
If `snip=TRUE`

(the default), such segments are cut into pieces by the
boundary of `j`

, and those pieces which lie inside the window
`ji`

are included in the resulting network.

Use `unmark`

to remove all the marks in a marked point
pattern, and `subset.lpp`

to remove only some columns of marks.

##### Value

A point pattern on a linear network (of class `"lpp"`

).

##### See Also

##### Examples

```
# NOT RUN {
# Chicago crimes data - remove cases of assault
chicago[marks(chicago) != "assault"]
# equivalent to subset(chicago, select=-assault)
# spatial window subset
B <- owin(c(350, 700), c(600, 1000))
plot(chicago)
plot(B, add=TRUE, lty=2, border="red", lwd=3)
op <- par(mfrow=c(1,2), mar=0.6+c(0,0,1,0))
plot(B, main="chicago[B, snip=FALSE]", lty=3, border="red")
plot(chicago[, B, snip=FALSE], add=TRUE)
plot(B, main="chicago[B, snip=TRUE]", lty=3, border="red")
plot(chicago[, B, snip=TRUE], add=TRUE)
par(op)
# }
```

*Documentation reproduced from package spatstat, version 1.57-1, License: GPL (>= 2)*