spdep (version 1.3-6)

subset.listw: Subset a spatial weights list

Description

The function subsets a spatial weights list, retaining objects for which the subset argument vector is TRUE. At present it will only subset non-general weights lists (that is those created by nb2listw with glist=NULL).

Usage

# S3 method for listw
subset(x, subset, zero.policy = attr(x, "zero.policy"), ...)

Value

The function returns an object of class listw with component style the same as the input object, component neighbours a list of integer vectors containing neighbour region number ids (compacted to run from 1:number of regions in subset), and component weights as the weights computed for neighbours using style. If no-neighbour observations are created by subsetting and zero.policy in the input weights object was FALSE, it will be set to TRUE and a warning issued.

Arguments

x

an object of class listw

subset

logical expression

zero.policy

default attr(x, "zero.policy") as set when x was created, if attribute not set, use global option value; if FALSE stop with error for any empty neighbour sets, if TRUE permit the weights list to be formed with zero-length weights vectors - passed through to nb2listw

...

generic function pass-through

Author

Roger Bivand

See Also

nb2listw, subset.nb

Examples

col.gal.nb <- read.gal(system.file("weights/columbus.gal", package="spData")[1])
to.be.dropped <- c(31, 34, 36, 39, 42, 46)
pre <- nb2listw(col.gal.nb)
print(pre)
post <- subset(pre, !(1:length(col.gal.nb) %in% to.be.dropped))
print(post)
columbus <- st_read(system.file("shapes/columbus.gpkg", package="spData")[1], quiet=TRUE)
nb <- poly2nb(columbus)
lw <- nb2listw(nb, style="W")
attr(lw, "zero.policy")
(lwa <- subset(lw, 1:nrow(columbus) != c(21)))
attr(lwa, "zero.policy")
(lwb <- subset(lw, !(1:nrow(columbus) %in% c(21, 36, 39))))
attr(lwb, "zero.policy")