`subset.listw.Rd`

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`

).

```
# S3 method for listw
subset(x, subset, zero.policy = NULL, ...)
```

- x
an object of class

`listw`

- subset
logical expression

- zero.policy
default NULL, 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

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`

.

```
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)
#> Characteristics of weights list object:
#> Neighbour list object:
#> Number of regions: 49
#> Number of nonzero links: 230
#> Percentage nonzero weights: 9.579342
#> Average number of links: 4.693878
#>
#> Weights style: W
#> Weights constants summary:
#> n nn S0 S1 S2
#> W 49 2401 49 23.48489 204.6687
post <- subset(pre, !(1:length(col.gal.nb) %in% to.be.dropped))
print(post)
#> Characteristics of weights list object:
#> Neighbour list object:
#> Number of regions: 43
#> Number of nonzero links: 212
#> Percentage nonzero weights: 11.46566
#> Average number of links: 4.930233
#>
#> Weights style: W
#> Weights constants summary:
#> n nn S0 S1 S2
#> W 43 1849 43 19.26584 178.4604
```