ifMissing: Take Measures in Case of Nonexisting Target Files

In Orcs: Omnidirectional R Code Snippets

Take Measures in Case of Nonexisting Target Files

Description

If a target file already exists, it is simply being imported into R. However, if the specified target file does not exist, it is first created by a user-defined function and subsequently returned, thus rendering explicit calls to file.exists() unnecessary.

Usage

ifMissing(ofl, fun0 = terra::rast, fun1 = terra::writeRaster, arg1, ...)

Arguments

ofl	Target file name as character.
fun0	If 'ofl' exists, function to be applied to it. Defaults to terra::rast()).
fun1	If 'ofl' does not exist, function used to create it. Defaults to terra::writeRaster()).
arg1	Argument in 'fun1' (as character) that corresponds to 'ofl', e.g. 'filename' in terra::writeRaster() or 'file' in utils::write.table(). If missing (default), the target file name passed to 'fun1' needs to be explicitly included via '...'.
...	Additional arguments passed to 'fun0' and 'fun1'.

Value

If 'ofl' has already existed, the contents of 'ofl' derived from 'fun0'; else the output resultant from 'fun1'.

Author(s)

Florian Detsch

See Also

file.exists(), do.call().

Examples

# simply import existing file
logo <- system.file("ex/logo.tif", package = "terra")
s <- ifMissing(logo) 

# create nonexisting file and import it afterwards
logo2 <- file.path(tempdir(), "rlogo.tif")
s2 <- ifMissing(logo2, arg1 = "filename", x = s, datatype = "INT1U")

# this also works with text files and more sophisticated custom functions
fun = function(x, file = "", ...) {
  write.csv(x, file, ...)
  read.csv(file)
}

data(iris)
ofl <- file.path(tempdir(), "iris.csv")
iris2 <- ifMissing(ofl, fun1 = fun, x = iris, file = ofl, quote = FALSE, row.names = FALSE)

Orcs documentation built on Jan. 6, 2023, 5:14 p.m.