SSN2 (version 0.2.1)

ssn_subset: Subset an SSN object

Description

Returns an SSN object that has been subset based on a logical expression.

Usage

ssn_subset(ssn, path, subset, clip = FALSE, overwrite = FALSE)

Value

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.

Arguments

ssn

An SSN object.

path

The filepath to the .ssn folder, in string format, where the subset SSN will be saved.

subset

A logical expression indicating which features to keep.

clip

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.

overwrite

If TRUE, overwrite the folder specified in path if it exists. Default = FALSE.

Details

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.

Examples

## 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
)