R devel - Dec 2016 - unlist strips date class

Is this a bug?
> unlist(list(as.Date("2015-01-01")))
[1] 16436

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On 2 December 2016 at 10:45, Kenny Bell wrote:
| Is this a bug?
| 
| > unlist(list(as.Date("2015-01-01")))
| [1] 16436

Not really, it is documented.

S3 classes operate via an attribute tag, and attributes get dropped by
certain base functions. I must have hit something like the following about a
thousand times by now:

R> for (i in as.Date("2015-01-01")+ 0:2) print(i)
[1] 16436
[1] 16437
[1] 16438
R>

Live and learn.

Dirk

-- 
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org

Hi,

On 12/02/2016 10:45 AM, Kenny Bell wrote:
> Is this a bug?
>
>> unlist(list(as.Date("2015-01-01")))
> [1] 16436
Good question.

More generally one might reasonably expect 'unlist(x)' to be equivalent
to 'do.call(c, x)' on a list 'x' where all the list elements are
atomic
vectors:

   x <- list(1:3, letters[1:2])
   unlist(x)
   # [1] "1" "2" "3" "a" "b"
   do.call(c, x)
   # [1] "1" "2" "3" "a" "b"

However, if the list contains dates:

   x <- list(as.Date("2015-01-01") + 0:2,
as.Date("2016-12-02"))
   unlist(x)
   # [1] 16436 16437 16438 17137
   do.call(c, x)
   # [1] "2015-01-01" "2015-01-02" "2015-01-03"
"2016-12-02"

then 'unlist(x)' drops the attributes and 'do.call(c, x)' does
not.

And if the list contains factors:

   x <- list(factor("Z"), factor(c("a", "Z",
"b")))
   unlist(x)
   # [1] Z a Z b
   # Levels: Z a b
   do.call(c, x)
   # [1] 1 1 3 2

then it's the other way around. Also note that the fact that the first
2 numbers in the result of 'do.call(c, x)' are the same is
confusing/misleading. Hard to see how this result could be useful
to anybody.

These inconsistencies might well be documented but hopefully they can
be addressed.

Cheers,
H.

-- 
Herv? Pag?s

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages at fredhutch.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319

On 02 Dec 2016, at 23:13 , Herv? Pag?s <hpages at fredhutch.org> wrote:
> More generally one might reasonably expect 'unlist(x)' to be
equivalent
> to 'do.call(c, x)' on a list 'x' where all the list
elements are atomic
> vectors:
Well, both are generic, and e.g. there is no "Date" method for
unlist(), but there is for c(). It is not clear that the two should be kept in
lockstep and there is certainly no mechanism to enforce that.

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com