[Rd] subset data.frame at C level

[Morgan Morgan]

Thank you Jim for the feedback.

I actually implemented it the way I describe it in my first email and it
seems fast enough for me.

Just to give a bit of context I will need it at some point in package kit.
I also implemented subset by row which I actually need more as I am working
on a faster version of the unique and duplicated function. The function
unique is particularly slow for data.frame. So far I got a 100x speedup.

Best regards
Morgan


On Tue, 23 Jun 2020, 21:11 Jim Hester, <james.f.hester using gmail.com> wrote:

> It looks to me like internally .subset2 uses `get1index()`, but this
> function is declared in Defn.h, which AFAIK is not part of the exported R
> API.
>
>  Looking at the code for `get1index()` it looks like it just loops over
> the (translated) names, so I guess I just do that [0].
>
> [0]:
> https://github.com/r-devel/r-svn/blob/1ff1d4197495a6ee1e1d88348a03ff841fd27608/src/main/subscript.c#L226-L235
>
> On Wed, Jun 17, 2020 at 6:11 AM Morgan Morgan <morgan.emailbox using gmail.com>
> wrote:
>
>> Hi,
>>
>> Hope you are well.
>>
>> I was wondering if there is a function at C level that is equivalent to
>> mtcars$carb or .subset2(mtcars, "carb").
>>
>> If I have the index of the column then the answer would be VECTOR_ELT(df,
>> asInteger(idx)) but I was wondering if there is a way to do it directly
>> from the name of the column without having to loop over columns names to
>> find the index?
>>
>> Thank you
>> Best regards
>> Morgan
>>
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