Hi,
I have a function f <- function(..., func){ something }, where func is a
function of the form function(...). ?I would like to pass func all the arguments
passed to f except the last. ?I know that I can manipulate the variable number
of arguments passed to f by converting ... to a list, i.e., arglist <-
list(...). ?But how do I pass func the first n-1 list items of arglist (n <-
length(arglist)), as n-1 arguments, not as one list of n-1 items?
Regards,
Richard
Richard R. Liu
richard.liu at pueo-owl.ch
How to convert a list to a ... argument for a function
3 messages · Richard R. Liu, Duncan Murdoch, Charles C. Berry
On 05/10/2010 2:23 PM, Richard R. Liu wrote:
Hi,
I have a function f<- function(..., func){ something }, where func is a
function of the form function(...). I would like to pass func all the arguments
passed to f except the last. I know that I can manipulate the variable number
of arguments passed to f by converting ... to a list, i.e., arglist<-
list(...). But how do I pass func the first n-1 list items of arglist (n<-
length(arglist)), as n-1 arguments, not as one list of n-1 items?
Do you know the name of the last one? If so, just declare it as an argument to f, and it won't be caught by ... . Do you know how many arguments there are? Then the barely documented ..1, ..2 etc might work for you. Otherwise, convert it to a list, and use do.call(func, args), where args is the list without the last element. Duncan Murdoch
On Tue, 5 Oct 2010, Richard R. Liu wrote:
Hi,
I have a function f <- function(..., func){ something }, where func is a
function of the form function(...). ??I would like to pass func all the arguments
passed to f except the last. ??I know that I can manipulate the variable number
of arguments passed to f by converting ... to a list, i.e., arglist <-
list(...). ??But how do I pass func the first n-1 list items of arglist (n <-
length(arglist)), as n-1 arguments, not as one list of n-1 items?
One way:
foo <- function(...,func){
mc <- match.call()
mc[[1]] <-mc$func
mc$func <- NULL
mc[[ length(mc) ]] <- NULL
eval(mc) }
foo(1,2,3,4,func=c)
foo(1,2,4,3,func=sum)
or perhaps you meant like this:
foo <- function(...,func){
mc <- match.call()
mc[[1]] <-mc$func
mc$func <- NULL
eval(mc) }
foo(1,2,3,4,func=c)
foo(1,2,4,3,func=sum)
HTH,
Chuck
Regards, Richard Richard R. Liu richard.liu at pueo-owl.ch
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901