[Rd] [ALTREP] What is the meaning of the return value of Is_sorted and No_NA function?

[Wang Jiefei]

Hi,

I've found the answers to my questions:

1. For sort function, here are some macros defined in Rinternal.h:
/* ALTREP sorting support */
enum {SORTED_DECR_NA_1ST = -2,
      SORTED_DECR = -1,
      UNKNOWN_SORTEDNESS = INT_MIN, /*INT_MIN is NA_INTEGER! */
      SORTED_INCR = 1,
      SORTED_INCR_NA_1ST = 2,
      KNOWN_UNSORTED = 0};

The macro names are pretty self-explanatory. The current implementation
only supports the ascending sort.

2. For anyNA, it goes to(Real SEXP)

===========coerce.c===========
if(REAL_NO_NA(x))
   return FALSE;
ITERATE_BY_REGION(x, xD, i, nbatch, double, REAL, {
for (int k = 0; k < nbatch; k++)
   if (ISNAN(xD[k]))
return TRUE;
   });

===========altrep.c===========
int REAL_NO_NA(SEXP x)
{
    return ALTREP(x) ? ALTREAL_DISPATCH(No_NA, x) : 0;
}

If the argument x is not an ALTREP, the function will return 0, and a
default method will be used, so there is no way to return true without loop
over the argument x right now. I hope this could be changed in the future.

Best,
Jiefei





On Tue, Sep 3, 2019 at 2:49 PM Wang Jiefei <szwjf08 using gmail.com> wrote:

> Hi,
>
>
>
> I would like to figure out the meaning of the return value of these two
> functions. Here are the default definitions I find from R source code:
>
>
>
> static int altreal_Is_sorted_default(SEXP x) { return UNKNOWN_SORTEDNESS;
> }
>
> static int altreal_No_NA_default(SEXP x) { return 0; }
>
> I guess the macro *UNKNOWN_SORTEDNESS *in *Is_sorted* and 0 in *No_NA *simply means
> unknown sorted/NA status of the vector, so R will loop over the vector and
> find the answer. However, what should we return in these functions to
> indicate whether the vector has been sorted/ contains NA? My initial guess
> is 0/1 but since *NA_NA *uses 0 as its default value so it will be
> ambiguous. Are there any macros to define yes/no return values for these
> functions? I would appreciate any thought here.
>
>
>
> Best,
>
> Jiefei
>
>
>

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