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Assign Varying Set of Values Passed at the Command Line or Interactively

Source: R/cmd_assign.R
cmd_assign_collect.Rd

Assign names to values in the global environment, like cmd_assign(), but without specifying the number of values in advance. Values for unnamed command line arguments are collected into a single character vector.

cmd_assign_collect_quiet() is identical to cmd_assign_collect() except that it does not print progress messages to the console.

Usage

cmd_assign_collect(...)

cmd_assign_collect_quiet(...)

Arguments

...

Name-value pairs.

Value

cmd_assign_collect() is called for its side effect, which is to create objects in the global environment. However, cmd_assign_collect() also invisibly returns a named list of objects.

Matching names and values

cmd_assign_collect(), like cmd_assign(), starts by processing named command line arguments (i.e. arguments of the form --n_draw=100). Unlike cmd_assign(), however, cmd_assign_collect() puts all the values that are left over into a single character vector. This vector can be any length, including zero. cmd_assign_collect() must contain a single name-value pair that is not used for named command line arguments. cmd_assign_collect() assigns the name from this name-value to the character vector.

If, for instance, the script combine.R contains

cmd_assign_collect(
  .files = c("data/a.csv", "data/b.csv", "out/combined.rds"),
  use_log = TRUE
)

and if combine.R is run from the command line using

Rscript combine.R \
  data/a.csv \
  data/c.csv \
  out/combined.rds \
  --use_log=TRUE

then use_log will be assigned the value TRUE and .files will be assigned the value c("data/a.csv", "data/c.csv", "out/combined.rds").

Processing the vector of unnamed arguments

The R script in which cmd_assign_collect() is called has responsibility for processing the character vector of values from unnamed command line arguments. The call to cmd_assign_collect() above, for instance, might be followed by statements such as

.inputs <- head(.files, -1)
.out <- tail(.files, 1)
inputs <- lapply(.inputs, read.csv)

Use cmd_assign() where possible

cmd_assign_collect() is more flexible than cmd_assign(), in that it does not require the number, name, or type of values to be specified in advance. But if these things are in fact known in advance, then it is good practice to document and test for them, which is what cmd_assign() does.

See also

Examples

if (interactive()) {
  cmd_assign_collect(
    files = c("data/x.csv", "data/y.csv"),
    use_log = TRUE
  )
}