Returns an SSN object that has been subset based on a
logical expression.
ssn_subset(ssn, path, subset, clip = FALSE, overwrite = FALSE)An SSN object.
The filepath to the .ssn folder, in string format,
where the subset SSN will be saved.
A logical expression indicating which features to keep.
If TRUE, create a subset of the edges and
prediction sites, based on the same logical expression used to
subset the observed sites. Default = FALSE.
If TRUE, overwrite the folder specified in
path if it exists. Default = FALSE.
an object of class SSN, which is stored locally in the .ssn
directory specified in path. It also creates and
stores an SQLite database, binaryID.db, within the .ssn
directory.
This function creates a subset of the original SSN
object based on a logical expression defined in the subset
argument. The subset argument is treated as an expression
within ssn_subset() and so the full argument is not a
string; although values in factor or character format will still
require quotes (see examples). If clip = TRUE, then the
columns referred to in subset must be present in the edges
and all of the prediction datasets (if present in the SSN
object). Note that features with missing values in the subset
expression are treated as false and are not included in the
subset SSN object.
Once the subset SSN object has been written to the local
directory, it is re-imported using
ssn_import. During this process, the
binaryID.db is recreated. If distance matrices exist in the
original SSN object, they are not copied or recalculated
for the new SSN object. Users will need to run the
ssn_create_distmat to create the distance
matrices before fitting models to the data in the subset
SSN.
## Import SSN object
copy_lsn_to_temp() ## Only needed for this example
mf04p <- ssn_import(paste0(tempdir(), "/MiddleFork04.ssn"),
predpts = "pred1km",
overwrite = TRUE
)
## Subset SSN observations, edges, and prediction sites on network 1
ssn.sub1 <- ssn_subset(mf04p,
path = paste0(tempdir(), "/subset1.ssn"),
subset = netID == 1, clip = TRUE,
overwrite = TRUE
)
## Subset SSN observations, removing two sites
ssn.sub2 <- ssn_subset(mf04p,
path = paste0(tempdir(), "/subset2.ssn"),
subset = !COMID %in% c("23519461", "23519365"),
overwrite = TRUE
)