[R] holding argument(s) fixed within lapply

[Benjamin Tyner]

|Hello,

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
|