ifMissing: 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, ...)

Value

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

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'.

Author

Florian Detsch

Examples

Run this code

# 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)