# split.ppp

##### Divide Point Pattern into Sub-patterns

Divides a point pattern into several sub-patterns, according to their marks, or according to any user-specified grouping.

##### Usage

```
## S3 method for class 'ppp':
split(x, f = marks(x), drop=FALSE, un=NULL, ...)
## S3 method for class 'ppp':
split(x, f = marks(x), drop=FALSE, un=missing(f), ...) <- value
```

##### Arguments

- x
- A two-dimensional point pattern.
An object of class
`"ppp"`

. - f
- Data determining the grouping. Either a factor, a pixel image with factor values, or a tessellation.
- drop
- Logical. Determines whether empty groups will be deleted.
- un
- Logical. Determines whether the resulting subpatterns will be unmarked (i.e. whether marks will be removed from the points in each subpattern).
- ...
- Other arguments are ignored.
- value
- List of point patterns.

##### Details

The function `split.ppp`

divides up the points of the point pattern `x`

into several sub-patterns according to the values of `f`

.
The result is a list of point patterns.
The argument `f`

may be

- a factor, of length equal to the number of points in
`x`

. The levels of`f`

determine the destination of each point in`x`

. The`i`

th point of`x`

will be placed in the sub-pattern`split.ppp(x)$l`

where`l = f[i]`

. - a pixel image (object of class
`"im"`

) with factor values. The pixel value of`f`

at each point of`x`

will be used as the classifying variable. - a tessellation (object of class
`"tess"`

). Each point of`x`

will be classified according to the tile of the tessellation into which it falls.

`f`

is missing, then `x`

must be a multitype point pattern
(a marked point pattern whose marks vector is a factor).
Then the effect is that the points of each type
are separated into different point patterns. Some of the sub-patterns created by the split
may be empty. If `drop=TRUE`

, then empty sub-patterns will
be deleted from the list. If `drop=FALSE`

then they are retained.

The argument `un`

determines how to handle marks
in the case where `x`

is a marked point pattern.
If `un=TRUE`

then the marks of the
points will be discarded when they are split into groups,
while if `un=FALSE`

then the marks will be retained.
The result of `split.ppp`

has class `"splitppp"`

and can be plotted using `plot.splitppp`

.

The assignment function `split<-.ppp`

updates the point pattern `x`

so that
it satisfies `split(x, f, drop, un) = value`

. The argument `value`

is expected to be a list of point patterns, one for each level of
`f`

. These point patterns are expected to be compatible with the
type of data in the original pattern `x`

.

Splitting can also be undone by the function `superimpose`

.

##### Value

- The value of
`split.ppp`

is a list of point patterns. The components of the list are named by the levels of`f`

. The list also has the class`"splitppp"`

.The assignment form

`split<-.ppp`

returns the updated point pattern`x`

.

##### See Also

##### Examples

```
# (1) Splitting by marks
# Multitype point pattern: separate into types
data(amacrine)
u <- split(amacrine)
# plot them
plot(split(amacrine))
# the following are equivalent:
amon <- split(amacrine)$on
amon <- unmark(amacrine[amacrine$marks == "on"])
# the following are equivalent:
amon <- split(amacrine, un=FALSE)$on
amon <- amacrine[amacrine$marks == "on"]
# Scramble the locations of the 'on' cells
u <- split(amacrine)
u$on <- runifpoint(amon$n, amon$window)
split(amacrine) <- u
# Point pattern with continuous marks
data(longleaf)
<testonly># smaller dataset
longleaf <- longleaf[seq(1, longleaf$n, by=80)]</testonly>
# cut the range of tree diameters into three intervals
# using cut.ppp
long3 <- cut(longleaf, breaks=3)
# now split them
long3split <- split(long3)
# (2) Splitting by a factor
# Unmarked point pattern
data(swedishpines)
# cut & split according to nearest neighbour distance
f <- cut(nndist(swedishpines), 3)
u <- split(swedishpines, f)
# (3) Splitting over a tessellation
tes <- tess(xgrid=seq(0,96,length=5),ygrid=seq(0,100,length=5))
v <- split(swedishpines, tes)
```

*Documentation reproduced from package spatstat, version 1.16-2, License: GPL (>= 2)*