[datatable-help] Preserving comments in [.data.table?

[Matthew Dowle]

Hi. I didn't know about base::comment. Should use unknownr::unk(),
shouldn't I!

Please raise a new feature request, or add it to this one :

#2197 "A simple labels attribute like in the Hmisc package for variable
descriptions"
https://r-forge.r-project.org/tracker/index.php?func=detail&aid=2197&group_id=240&atid=978

Do we want labels, or comments, or both? Griffith Rees (cc'd)?

Since comment<- will copy the whole table, we'd need setcomment() [or
setlabel(), or both] to avoid that copy; adding to the set* family.

> PS: is stopifnot(identical(DT1[DT1]$A, DT1[DT1]$A.1)) a buglet?

Seems ok :

> DT1 <- data.table(id = seq.int(1, 10), A = LETTERS[1:10], key = "id")
> stopifnot(identical(DT1[DT1]$A, DT1[DT1]$A.1))
> comment(DT1$A) <- "A"
> stopifnot(identical(DT1[DT1]$A, DT1[DT1]$A.1))
Error: identical(DT1[DT1]$A, DT1[DT1]$A.1) is not TRUE
> str(DT1[DT1]$A)
 chr [1:10] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J"
> str(DT1[DT1]$A.1)
 atomic [1:10] A B C D ...
 - attr(*, "comment")= chr "A"


>
> On 11/09/12 09:47, I wrote:
>> I like comments, but [.data.table drops them, e.g.
>
> More specifically, it drops them for the 'outer' data.table but not the
> inner (!?) when doing the join:
>
> DT1 <- data.table(id = seq.int(1, 10), A = LETTERS[1:10], key = "id")
> comment(DT1$A) <- "A"
> DT2 <- data.table(id = seq.int(2, 10, 2), b = letters[1:5], key = "id")
> comment(DT2$b) <- "b"
> str(DT1[DT2]) # No comment on A
> str(DT2[DT1]) # No comment on b
>
> Allan
>
> PS: is stopifnot(identical(DT1[DT1]$A, DT1[DT1]$A.1)) a buglet?
>
>>
>> DT1 <- data.table(A = 1:10)
>> comment(DT1$A) <- "Documenting A column"
>> DT2 <- DT1[A %% 2]
>> stopifnot(identical(comment(DT1$A), comment(DT2$A)))
>>
>> Is there any way of preserving the comments? (My normal use case is
>> DT1 <- DT1[...] so copying from one to the other is a little ...
>> tedious?)
>>
>> Allan
>>
>
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