Thank you Blaser; this is helpful. On 03/13/2013 12:22 PM, Blaser Nello wrote: > One way is to use the do.call function. For example: > > ret2 <- lapply(X=mylist2, > FUN=do.call, > what=function(...) f2(y=Y, ...)) > > Best, > Nello > > -----Original Message----- > Date: Tue, 12 Mar 2013 22:37:52 -0400 > From: Benjamin Tyner <bty...@gmail.com> > To: r-help@r-project.org > Subject: Re: [R] holding argument(s) fixed within lapply > Message-ID: <513fe680.2070...@gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Apologies; resending in plain text... > > Given a function with several arguments, I would like to perform an > lapply (or equivalent) while holding one or more arguments fixed to some > common value, and I would like to do it in as elegant a fashion as > possible, without resorting to wrapping a separate wrapper for the > function if possible. Moreover I would also like it to work in cases > where one or more arguments to the original function has a default > binding. > > # Here is an example; the original function > f <- function(w, y, z){ w + y + z } > > # common value I would like y to take > Y <- 5 > > # I have a list of arguments for the lapply() > mylist <- list(one = list(w = 1, z = 2), > two = list(w = 3, z = 4) > ) > > # one way to do it involves a custom wrapper; I do not like this > method > ret <- lapply(FUN = function(x,...) f(w = x$w, z = x$z, ...), > X = mylist, > y = Y > ) > > # another way > ret <- lapply(FUN = with.default, > X = mylist, > expr = f(w, y = Y, z) > ) > > # yet another way > ret <- lapply(FUN = eval, > X = mylist, > expr = substitute(f(w, y = Y, z)) > ) > > # now, the part I'm stuck on is for a version of f where z has a > default binding > f2 <- function(w, y, z = 0){ w + y + z } > > # the same as mylist, but now z is optional > mylist2 <- list(one = list(w = 1), > two = list(w = 3, z = 4) > ) > > # undesired result (first element has length 0) > ret2 <- lapply(FUN = function(x,...) f2(w = x$w, z = x$z, ....), > X = mylist2, > y = Y > ) > > # errors out ('z' not found) > ret2 <- lapply(FUN = with.default, > X = mylist2, > expr = f2(w, y = Y, z) > ) > > # errors out again > ret2 <- lapply(FUN = eval, > X = mylist2, > expr = substitute(f2(w, y = Y, z)) > ) > > # not quite... > ret2 <- lapply(FUN = gtools::defmacro(y = Y, expr = f2(w, y = Y, > z)), > X = mylist2 > ) > > It seems like there are many ways to skin this cat; open to any and all > guidance others care to offer. > > Regards, > Ben >
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