[R] understanding as.list(substitute(...()))

[peter dalgaard]

> On 6 Oct 2020, at 09:22 , Dénes Tóth <toth.denes using kogentum.hu> wrote:
> 
> > foo <- function(...) substitute({...()})
> > foo(abc$de, fg[h], i)
> {
>   pairlist(abc$de, fg[h], i)
> }
> > foo(abc$de, fg[h], , i) # add a missing argument for extra fun
> {
>   as.pairlist(alist(abc$de, fg[h], , i))
> }
> 

The 2nd one here is actually an artifact of deparse(). The result is still a pairlist, just one that pairlist(....) cannot reproduce:

> e <- foo(abc$de, fg[h], , i) 
> e[[2]]
[[1]]
abc$de

[[2]]
fg[h]

[[3]]


[[4]]
i

> deparse(e[[2]])
[1] "as.pairlist(alist(abc$de, fg[h], , i))"
> dput(e[[2]])
as.pairlist(alist(abc$de, fg[h], , i))
> mode(e[[2]])
[1] "pairlist"
> mode(e[[2]][[3]])
[1] "name"

I.e. the list in e[2] contains the missing indicator (an empty name). (I'm slightly puzzled why we need the curlies to trigger a deparse, though) 



-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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