[Rd] Convert STRSXP or INTSXP to factor

[Martin Maechler]

>>>>> Gabriel Becker 
>>>>>     on Mon, 15 Jul 2019 13:29:28 -0700 writes:

    > Hi Morgan,
    > So if the goal  is output  identical to  calling factor, one thing youc an
    > do is construct  and evaluate a call to the R-level factor function. That
    > would work and  be guaranteed to meet your  requirement.

    > The factor function is implemented with R code,  without even any direct
    > calls down to C code, so there isn't any C level functionality already
    > there that you could try to hit directly.

    > If you really really needed to write it using only C (and not hitting the R
    > evaluator), I suppose you could. You'd need to do the following, I think:

        [... hoop jumping  ...]
        [... hoop jumping  ...]


    > Personally, unless there was a really compelling reason not to, I'd just do
    > the  create and evaluate an R-level call thing instead.

I'm strongly supporting that.  That's the only will not to have
to change your (potentially brittle) C code if  factor() or
as.factor() .. is tweaked in a future version of R.





    > On Mon, Jul 15, 2019 at 3:25 AM Morgan Morgan <morgan.emailbox using gmail.com>
    > wrote:

    >> Hi,
    >> 
    >> Using the R C PAI, is there a way to convert to convert STRSXP or INTSXP to
    >> factor.
    >> 
    >> The idea would be to do in C something similar to the "factor" function
    >> (example below):
    >> 
    >> > letters[1:5]
    >> # [1] "a" "b" "c" "d" "e"
    >> 
    >> > factor(letters[1:5])
    >> # [1] a b c d e
    >> # Levels: a b c d e
    >> 
    >> There is the function setAttrib the levels of a SXP however when returned
    >> to R the object is of type character not factor. Ideally what i would like
    >> to return from the C function is the same output as above when the input is
    >> of type character.
    >> 
    >> Please let me if you need more informations.
    >> Thank you
    >> Best regards
    >> Morgan
    >> 
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    >> 
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