Question

i have set some environment variables:

envir1 <- new.env()
assign("a", 7, envir=envir1)
assign("b", 8, envir=envir1)
assign("x", 9, envir=envir1)

now i have a list with some of this varibles and some numerics:

lis <- list(1,2, as.name("a"), 5, as.name("x"))

how can i get the numeric value in both ways, when it’s a variable name and when it’s a number

getNumbers2 <- function(li,pos) {
    ## Part where i dont know  
    return(li[[pos]]) ## dont works. the name of the variable is returned
}

getNumbers <- function(li,pos, env1) {
    environment(getNumbers2) <- env1
    getNumbers2(li,pos)
}

getNumbers(lis, 3, envir1)
a ## << wanna have 7 here

Answer 1

Why are you storing the "a" and "x" as an R symbol?:

R> str(l[[3]])
 symbol a

If you’d just done:

env1 <- new.env()
assign("a", 7, envir=env1)
assign("b", 8, envir=env1)
assign("x", 9, envir=env1)
ll <- list(1, 2, "a", 5, "x")

Then this

with(env1, get(ll[[3]]))

would have worked:

R> with(env1, get(ll[[3]]))
[1] 7

but that doesn’t work easily inside a function, because of scoping problems.

However, seeing as with(env1, get(ll[[3]])) works, you probably don’t need the function. Also note that get() takes an environment as an argument:

R> get(ll[[3]], envir = env1)
[1] 7

So we could write the function as

getNumbers <- function(obj, pos, env) {
    get(obj[[pos]], envir = env)
}

Which does work:

R> getNumbers(ll, 3, env1)
[1] 7

Edit: Just to be clear, if all that is required is to extract an object by name (the position bit threw me as that doesn’t make any sense), then, as @hadley mentions in a comment below, all we really need is to subset the environment using [[:

R> env1[[ll[[3]]]]
[1] 7

which, I suppose, if you want to wrap it in a functions would be

getNumbers <- function(obj, pos, env) {
    env[[obj[[pos]]]]
}

R> getNumbers(ll, 3, env1)
[1] 7