Return elements of list as independent objects in global environment

Question

I have a list, and would like to break the elements of the list into seperate objects in the global environment.

For example, I would like the list:

obj <- list(a=1:5, b=2:10, c=-5:5)

to be three seperate objects a, b, and c.

I tried to achieve this with:

lapply(obj, FUN = function(x) names(x)[1] <<- x[1])

But it failed, with Error in names(x)[1] <<- x[1] : object 'x' not found.

How might I achieve my aim?

score 72 · Accepted Answer · answered Dec 10 '12 at 09:17

72

There is special function for mapping list to environment:

> obj <- list(a=1:5, b=2:10, c=-5:5)
> ls()
[1] "obj"
> list2env(obj,globalenv())
<environment: R_GlobalEnv>
> ls()
[1] "a"   "b"   "c"   "obj"

P. S. It is my comment provided as an answer

answered Dec 10 '12 at 09:17

Gregory Demin

Tyler Rinker · Answer 2 · 2012-12-10T05:52:52.870

10

This also would work:

lapply(seq_along(obj), function(i) assign(names(obj)[i], obj[[i]], envir = .GlobalEnv))

edited Dec 10 '12 at 05:52

answered Dec 10 '12 at 05:45

Tyler Rinker

You might want `obj[[i]]` instead, so that you assign vectors, and not one element lists. – Marius Dec 10 '12 at 05:49
1

Please not Dason's does what you want as well with less headache. – Tyler Rinker Dec 10 '12 at 06:34
1

@ricardo, please take a look at Gregory's comment to your question. -- (the other) – Ricardo Saporta Dec 10 '12 at 07:23
I don't like to attach data, ever. Is there a good reason to break this rule? – ricardo Dec 10 '12 at 07:50
@ricardo Gregory's answer isn't using `attach` (which is a bad idea and why I don't recommend it). Then again if you don't like attaching data why are you doing what you want to do in the question instead of working directly with the list itself? – Dason Dec 10 '12 at 15:59
No shame in unchecking this answer and selecting Gregory's. – Tyler Rinker Dec 10 '12 at 16:19

score 1 · Answer 3 · answered Jul 22 '21 at 09:53

1

In case the list isn't yet a named list, we need to set names first, e.g. with incrementing letters.

obj2 <- list(1:5, 2:10, -5:5)

list2env(setNames(obj2, letters[seq(obj2)]), envir=.GlobalEnv)
ls()
# [1] "a"    "b"    "c"    "obj2"

answered Jul 22 '21 at 09:53

jay.sf

score -1 · Answer 4 · answered Dec 10 '12 at 05:36

-1

I don't recommend it but you could use attach

> obj <- list(a=1:5, b=2:10, c=-5:5)
> attach(obj)
> a
[1] 1 2 3 4 5
> b
[1]  2  3  4  5  6  7  8  9 10
> c
 [1] -5 -4 -3 -2 -1  0  1  2  3  4  5

answered Dec 10 '12 at 05:36

Dason

1

This does not what OP asked, it just attaches the object `obj` to the search path. That doesn't mean you assign the elements of the list to independent objects in the global environment. Gregory has the correct answer. – Joris Meys Dec 10 '12 at 12:35
@JorisMeys Sure but they never really said why they wanted to do this either. `attach` allows you to pretend like they're a part of the global environment (at least in simple cases) with very little work. With that said I definitely think Gregory's answer is the best out of the answers given. – Dason Dec 10 '12 at 14:49
I see why you mentioned it, but the use of `attach` poses a lot more problems than it solves, not in the least when you try to change one of the elements in the list. As said in the [R Style Guide](http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html#attach) : The possibilities for creating errors when using attach are numerous. Avoid it. – Joris Meys Dec 10 '12 at 15:07
@JorisMeys I agree. Which is why I don't recommend it. I also don't really like the whole idea posted in the question though. There are also dangers associated with Gregory's answer as well too – Dason Dec 10 '12 at 15:57

4 Answers4