match.arg.ext: Extended Argument Matching

Description

match.arg.ext matches arg against a set of candidate values as specified by choices; it extends match.arg() by allowing arg to be a numeric identifier of the choices.

Usage

match.arg.ext(
  arg,
  choices,
  base = 1,
  several.ok = FALSE,
  numeric = FALSE,
  ignore.case = FALSE
)

Value

If numeric is false and arg is a character string, the function returns the unabbreviated version of the unique partial match of arg if there is one; otherwise, an error is produced if several.ok is false, as per default. When several.ok is true and there is more than one match, all unabbreviated versions of matches are returned.

If numeric is false but arg is numeric, match.arg.ext returns name of the match corresponding to this index, counting from base; i.e. arg=base corresponds to choices[1].

If numeric is true, the function returns the numeric index(es) of the partial match of arg, counted from base to length(choices)+base-1. If arg is already numeric, the function only checks whether it falls into the valid range from arg to length(choices)+base-1 and returns arg.

Arguments

arg: a character string or numeric value
choices: a character vector of candidate values
base: numeric value, specifying the numeric index assigned to the first element of choices
several.ok: logical specifying if arg should be allowed to have more than one element
numeric: logical specifying if the function should return the numerical index (counting from base) of the matched argument, or, by default, its name
ignore.case: logical specifying if the matching should be case sensitive

Author

Alexander Brenning

Details

When choices are missing, they are obtained from a default setting for the formal argument arg of the function from which match.arg.ext was called.

Matching is done using pmatch() (indirectly through a call to match.arg(), so arg may be abbreviated.

If arg is numeric, it may take values between base and length(choices)+base-1. base=1 will give standard 1-based R indices, base=0 will give indices counted from zero as used to identify SAGA modules in library RSAGA.

Examples

Run this code

# Based on example from 'match.arg':
require(stats)
center <- function(x, type = c("mean", "median", "trimmed")) {
  type <- match.arg.ext(type,base=0)
  switch(type,
         mean = mean(x),
         median = median(x),
         trimmed = mean(x, trim = .1))
}
x <- rcauchy(10)
center(x, "t")       # Works
center(x, 2)         # Same, for base=0
center(x, "med")     # Works
center(x, 1)         # Same, for base=0
try(center(x, "m"))  # Error

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