R get objects' names from the list of objects

Question

I try to get an object's name from the list containing this object. I searched through similar questions and find some suggestions about using the deparse(substitute(object)) formula:

> my.list <- list(model.product, model.i, model.add)
> lapply(my.list, function(model) deparse(substitute(model)))

and the result is:

[[1]]
[1] "X[[1L]]"

[[2]]
[1] "X[[2L]]"

[[3]]
[1] "X[[3L]]"

whereas I want to obtain:

[1] "model.product", "model.i", "model.add"

Thank you in advance for being of some help!

Answer 1

You can write your own list() function so it behaves like data.frame(), i.e., uses the un-evaluated arg names as entry names:

List <- function(...) {
  names <- as.list(substitute(list(...)))[-1L]
  setNames(list(...), names)
}

my.list <- List(model.product, model.i, model.add)

Then you can just access the names via:

names(my.list)

Answer 2

names(my.list) #..............

Oh wait, you didn't actually create names did you? There is actually no "memory" for the list function. It returns a list with the values of its arguments but not from whence they came, unless you add names to the pairlist given as the argument.

Answer 3

You won't be able to extract the information that way once you've created my.list.

The underlying way R works is that expressions are not evaluated until they're needed; using deparse(substitute()) will only work before the expression has been evaluated. So:

deparse(substitute(list(model.product, model.i, model.add)))

should work, while yours doesn't.