[datatable-help] NA in joins

[Juan Manuel Truppia]

It might help, specially where data.table is compared to SQL. However, I
think that having merge (and maybe [.data.table) have an argument to avoid
NA matching. Is there a FR already created for this? I can create it
otherwise

On Thu, Sep 18, 2014 at 4:00 PM, Arunkumar Srinivasan <aragorn168b at gmail.com
> wrote:

> In base R `NA` matches `NA` alone, and `NaN` matches `NaN` alone:
> match(NA, c(1:5, NA))
> # [1] 6
>
> data.table matches, through binary search, by design, in the same way. And
> in `?match`, there's this line: "Exactly what matches what is to some
> extent a matter of definition." In some operations it may not make sense.
> But, by design, we do consider Inf = Inf, -Inf = -Inf, NaN = NaN and NA =
> NA always. Do you think it'd help tp state this explicitly in `?data.table`?
>
>
> Arun
>
> From: Juan Manuel Truppia <jmtruppia at gmail.com> <jmtruppia at gmail.com>
> Reply: Juan Manuel Truppia <jmtruppia at gmail.com>> <jmtruppia at gmail.com>
> Date: September 18, 2014 at 6:14:56 PM
> To: datatable-help at lists.r-forge.r-project.org
> <datatable-help at lists.r-forge.r-project.org>>
> <datatable-help at lists.r-forge.r-project.org>
> Subject:  [datatable-help] NA in joins
>
>  Hi, this must have been discussed before, but I couldn't find anything.
>
> In my opinion, NA shouldn't join with anything, including other NA (as to
> mirror what we expect from SQL, where NULL doesn't join with NULL).
>
> However, with data.table, NA matches other NA.
>
> I.e, this should return an empty data.table
>
> data.table(idx = NA_real_, key = "idx")[data.table(idx = NA_real_, val =
> "a", key = "idx"), nomatch = 0]
>
> Let's assume that we can't change this behavior, would it be possible to
> add a parameter to avoid NA matching NA in [.data.table and merge?
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