[R] with() and within() functions inside lapply() not seeing outside of its environment?

Pavel N. Krivitsky pavel at uow.edu.au
Tue Jan 7 16:35:03 CET 2014


I have a list of sublists, and I want to add and/or remove elements in
each sublist in accordance with a code snippet. I had thought that an
elegant way to do that is using a combination of lapply() and within().
However, the code in the within() call doesn't seem to be able to see
objects outside of it. For (a simplified) example,

f <- function(x){
  y <- list(y1=list())
  y <- lapply(y, within, {z<-x})

My understanding is that what should happen is that lapply() would

within(y[["y1"]], {z<-x}),

with 1 substituted for x, within() would notice that z has been assigned
1, returning list(z=1), which then gets put into a list as element named
"y1", so the function should ultimately return


What I get instead (on R 3.0.2 and current trunk, both on Linux) is

Error in eval(expr, envir, enclos) : object 'x' not found

Am I doing something wrong, or is this a bug?

                   Thanks in advance,

P.S. If I "hard-code" the value for x, i.e.,

f <- function(){
  y <- list(y1=list())
  y <- lapply(y, within, {z<-1})

it returns list(y1=list(z=1)) as expected.

P.P.S. with() has the same problem:

f <- function(x){
  y <- list(y1=list())
  w <- lapply(y, with, x)

produces the exact same error as within().

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