[R] list assignment syntax?

[Bert Gunter]

,,,But assigning to the global environment is a bad idea. You're just
asking for trouble -- overwriting without warning something that's
already there.

May I suggest a rule of thumb: When things are difficult or clumsy to
do in R, don't do them.

Of course this is not inviolable, but the OP's request may be one
instance where it applies.

-- Bert

On Fri, Mar 30, 2012 at 7:24 PM, Joshua Wiley <jwiley.psych at gmail.com> wrote:
> An idiom like this would also work.
>
> f <- function(a,b) list( data.frame(a+rnorm(20), b), loess( a ~ b) )
> lapply(seq_along(out <- f(1:20, 1:20)), function(i) assign(c("c",
> "d")[i], out[[i]], envir = .GlobalEnv))
>
>  It is not elegant if you are doing this regularly, but, I think,
> functions typically return lists of output rather than assigning to
> the global environment because presumably one function returns related
> objects so it makes sense for them to stay grouped in a list.  If the
> two steps really are unrelated, then use two functions.
>
> It seems like what you want is to have a function return each object
> not in a list but to the global environment, but you would like to be
> able to give them your own names (which makes sense).  If this is with
> your own functions, you could adapt them easily to accept names and
> then assign to global.
>
> f <- function(a,b, names = c("a", "b")) {
>  assign(names[1], data.frame(a + rnorm(20), b), envir = .GlobalEnv)
>  assign(names[2], loess(a ~ b), envir = .GlobalEnv)
> }
> f(1:20, 1:20, c("c", "d"))
>
> I'm not arguing against Gabor's list function, just tossing out a few
> other ideas.  I am not familiar with perl, but in R I am used to the
> thing on the left being what is assigned to; the list[a, b] assigning
> to global is counterintuitive to me personally.
>
> Given that this works:
>
> .GlobalEnv[["a"]] <- 1
> a
>
> I was hoping that:
>
> .GlobalEnv[c("c", "d")] <- f(1:20, 1:20)
>
> would also, but alas environments are not subsettable.  Interesting question.
>
> Cheers,
>
> Josh
>
> On Fri, Mar 30, 2012 at 6:26 PM, ivo welch <ivo.welch at gmail.com> wrote:
>> thanks, everyone.  I should have been clearer (as always).  I used the
>> numbers as an example only.  I am aware that I can put numbers into
>> vectors and get nice R syntax.  my problem is that I usually want to
>> return multiple and/or mixed objects, such as multiple data frames.  I
>> should have given as an example something like
>>
>>   f <- function(a,b) list( data.frame(a+rnorm(20), b), loess( a ~ b) )
>>
>> weidong---yes, nice syntax, but I don't want to invoke f() twice.
>>
>> peter---I don't think your unlist syntax works.  I tried it.
>>
>> gabor---#1-#3 work, but aren't what I really want.  #4 is exactly what
>> I wanted.  can list[] be added into the standard core R as a feature?
>> it would seem like a natural part of the syntax for functions
>> returning multiple values.
>>
>> justin---mea culpa.
>>
>> regards,
>>
>> /iaw
>> ----
>> Ivo Welch (ivo.welch at gmail.com)
>>
>>
>>
>> On Fri, Mar 30, 2012 at 5:08 PM, Justin Haynes <jtor14 at gmail.com> wrote:
>>> You can also take a look at
>>>
>>> http://stackoverflow.com/questions/7519790/assign-multiple-new-variables-in-a-single-line-in-r
>>>
>>> which has some additional solutions.
>>>
>>>
>>>
>>> On Fri, Mar 30, 2012 at 4:49 PM, Peter Ehlers <ehlers at ucalgary.ca> wrote:
>>>> On 2012-03-30 15:40, ivo welch wrote:
>>>>>
>>>>> Dear R wizards:  is there a clean way to assign to elements in a list?
>>>>>  what I would like to do, in pseudo R+perl notation is
>>>>>
>>>>>  f<- function(a,b) list(a+b,a-b)
>>>>>  (c,d)<- f(1,2)
>>>>>
>>>>> and have c be assigned 1+2 and d be assigned 1-2.  right now, I use the
>>>>> clunky
>>>>>
>>>>>   x<- f(1,2
>>>>>   c<- x[[1]]
>>>>>   d<- x[[2]]
>>>>>   rm(x)
>>>>>
>>>>> which seems awful.  is there a nicer syntax?
>>>>>
>>>>> regards, /iaw
>>>>> ----
>>>>> Ivo Welch (ivo.welch at brown.edu, ivo.welch at gmail.com)
>>>>>
>>>>
>>>> I must be missing something. Why not just assign to a
>>>> vector instead of a list?
>>>>
>>>>  f<- function(a,b) c(a+b,a-b)
>>>>
>>>> If it's imperative that f return a list, then you
>>>> could use
>>>>
>>>>  (c, d) <- unlist(f(a, b))
>>>>
>>>> to get vector (c, d).
>>>>
>>>> Peter Ehlers
>>>>
>>>>
>>>> ______________________________________________
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>>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Joshua Wiley
> Ph.D. Student, Health Psychology
> Programmer Analyst II, Statistical Consulting Group
> University of California, Los Angeles
> https://joshuawiley.com/
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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