subset.lpp {spatstat.linnet}

Subset of Point Pattern Satisfying A Condition

Description

Given a point pattern on a linear network, return the subset of points which satisfy a specified condition.

Usage

## S3 method for class 'lpp'
subset(x, subset, select, drop=FALSE, ...)

Arguments

x

A point pattern on a linear network (object of class "lpp").

subset

Logical expression indicating which points are to be kept. The expression may involve the names of spatial coordinates (x, y), network coordinates (seg, tp), the marks, and (if there is more than one column of marks) the names of individual columns of marks. Missing values are taken as false. See Details.

select

Expression indicating which columns of marks should be kept. The names of columns of marks can be used in this expression, and will be treated as if they were column indices. See Details.

drop

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

...

Ignored.

Details

This is a method for the generic function subset. It extracts the subset of points of x that satisfy the logical expression subset, and retains only the columns of marks that are specified by the expression select. The result is always a point pattern, with the same window as x.

The argument subset determines the subset of points that will be extracted. It should be a logical expression. It may involve the variable names x and y representing the Cartesian coordinates; the names of other spatial coordinates or local coordinates; the name marks representing the marks; and (if there is more than one column of marks) the names of individual columns of marks. The default is to keep all points.

The argument select determines which columns of marks will be retained (if there are several columns of marks). It should be an expression involving the names of columns of marks (which will be interpreted as integers representing the positions of these columns). For example if there are columns of marks named A to Z, then select=D:F is a valid expression and means that columns D, E and F will be retained. Similarly select=-(A:C) is valid and means that columns A to C will be deleted. The default is to retain all columns.

Setting subset=FALSE will produce an empty point pattern (i.e. containing zero points) in the same window as x. Setting select=FALSE or select= -marks will remove all the marks from x.

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

The result is always a point pattern, of the same class as x. Spatial coordinates (and local coordinates) are always retained. To extract only some columns of marks or coordinates as a data frame, use subset(as.data.frame(x), ...)

Value

A point pattern of the same class as x, in the same spatial window as x. The result is a subset of x, possibly with some columns of marks removed.

Other kinds of subset arguments

Alternatively the argument subset can be any kind of subset index acceptable to [.lpp. This argument selects which points of x will be retained.

Warning: if the argument subset is a window, this is interpreted as specifying the subset of points that fall inside that window, but the resulting point pattern has the same window as the original pattern x.

Author(s)

Adrian Baddeley [e-mail], Rolf Turner [e-mail] and Ege Rubak [e-mail].

See Also

subset.ppp, [.lpp.

Examples

 v <- subset(chicago, x + y > 1100 & marks == "assault")

 vv <- subset(chicago, x + y > 1100 & marks == "assault", drop=TRUE)