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One of my in-progress functions calls grep() with value = TRUE hard-coded. I'd like to pass all of the further arguments except value to grep() through with .... The two functions below are tests I've done so far, neither of which gets the job done.

What is the best way to exclude one or more further arguments when using ... ?

Practice function 1:

f <- function(pattern, x, ...)
{
    dots <- list(...)
    if('value' %in% names(dots)) 
        dots <- dots[!grepl('value', names(dots))]
    grep(pattern, x, value = TRUE, ...)
}

XX <- c('bct', 'abc', 'fds', 'ddabcff', 'jkl')    
## test f()
f('abc', XX, value = TRUE) ## to test the error if user enters 'value' argument
# Error in grep(pattern, x, value = TRUE, ...) : 
#     formal argument "value" matched by multiple actual arguments
f('abc', XX, invert = TRUE)
# [1] "bct" "fds" "jkl"
f('ABC', XX, ignore.case = TRUE)
# [1] "abc"     "ddabcff"

Practice function 2:

h <- function(pattern, x, ...) x[grep(pattern, x, ...)]    
## test h()
h('abc', XX, value = TRUE)
# [1] NA NA
h('abc', XX, invert = TRUE)
# [1] "bct" "fds" "jkl"
h('ABC', XX, ignore.case = TRUE)
# [1] "abc"     "ddabcff"
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1 Answer

You can combine Curry with do.call:

require(functional)
f <- function(pattern, x, ...)
{
  dots <- list(...)
  dots <- dots[!grepl('value', names(dots))]
  do.call(Curry(grep, pattern=pattern, x=x, value=TRUE), dots)
}

Curry provides the known arguments, and dots supplies everything other than "value" in ....


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