[datatable-help] dcast.data.table loses column classes when column is date

[Juan Manuel Truppia]

Posted here https://github.com/Rdatatable/datatable/issues/688

However, I couldn't tag it as a bug (didn't find the option to add a
label, sorry!)

On Mon, Jun 9, 2014 at 6:29 PM, Arunkumar Srinivasan
<aragorn168b at gmail.com> wrote:
> Juan,
>
> On how to report a bug:
> 1) Go to https://github.com and create an account, if you don't already have
> one.
> 2) Go to our project page, while signed in:
> https://github.com/Rdatatable/datatable
> 3) Click "Issues" on the right side of the page.
> 4) This issue doesn't already exist. So, hit "New issue" (green button on
> the right).
> 5) Provide a title. Fill the body - remember you can format code using
> Markdown (as well as Github flavoured markdown). For example, to write
> R-code, you can do:
>
> ```S
> your R-code
> ```
>
> The S is the lexer type (for highlighting code using Github flavoured
> markdown).
> 6) Add a label (equivalent of tag or tracker type in R-Forge) by clicking on
> "bug" on the right side.
> 7) Preview your post, if you want to. Then click "Submit new issue".
>
> ---
>
> On the bug itself: This is because `reshape2:::dcast` doesn't preserve
> attributes. And we wanted to be consistent with their result at the time of
> writing.
> However, since that time, `reshape2` has obtained newer implementation of
> "melt", written by Kevin Ushey, where attributes are preserved as long as
> all the columns that you're asking for to be "molten" are of the same type.
> But this doesn't happen for "factors" by default because that might break
> existing code - and therefore obtained a new argument "factorsAsStrings",
> IIUC. I personally find these things adding a layer of complexity. But
> that's the case with "melt".
>
> It's really hard to tell from reshape2's ?melt or ?cast what's the case
> regarding attributes. But my guess is that we should, starting with your
> post, try to define what's what and document it instead of relying entirely
> on being consistent with reshape2's behaviour, as we do already differ from
> reshape2 already slightly.
>
> We're very much younger than reshape2's melt/cast. So, I think we might be
> able to rectify these things on consistency and rules relatively easier.
>
> Arun
>
> From: Juan Manuel Truppia jmtruppia at gmail.com
> Reply: Juan Manuel Truppia jmtruppia at gmail.com
> Date: June 9, 2014 at 10:13:05 PM
> To: datatable-help at lists.r-forge.r-project.org
> datatable-help at lists.r-forge.r-project.org
> Subject:  [datatable-help] dcast.data.table loses column classes when column
> is date
>
> Here is a reproducible example
>
> dcast.data.table(data = data.table(id = c(1,1,2,2), ty =
> c("a","b","a","b"), da = Sys.Date()), formula = id ~ ty)
>
> I don't know how to report a bug, if someone guides me, I'll be much obliged
>
> Thanks!
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