[R] Putting a NULL in a list (as cannot pass NA to C++)

[Charles C. Berry]

On Mon, 3 Dec 2007, Rees, David  wrote:

> Hi,
>
> If I do the following I can have a NULL in a list
>
>> x <- list( 1, list(3,NULL,4), 5 )
>> x
> [[1]]
> [1] 1
>
> [[2]]
> [[2]][[1]]
> [1] 3
>
> [[2]][[2]]
> NULL
>
> [[2]][[3]]
> [1] 4
>
>
> [[3]]
> [1] 5
>
> This is a good thing for me as it can be passed through into C++ where I
> can know the value is missing. (Can't seem to detect a NA from C++ for
> some reason. There is RF_isNull in the API but no RF_isNA that I can
> find!)

Is this what you were looking for?


Writing R Extensions

6.4 Missing and IEEE special values

A set of functions is provided to test for NA, Inf, -Inf and NaN. These 
functions are accessed via macros:

      ISNA(x)        True for R's NA only
      ISNAN(x)       True for R's NA and IEEE NaN
      R_FINITE(x)    False for Inf, -Inf, NA, NaN

HTH,

Chuck

p.s. grep '<something>' within R's include directory can quickly resolve 
questions like this.

>
> Is it possible to put a null in an already created list. e.g. now do
>
>> x[[2]][[2]] <- NULL
>> x
> [[1]]
> [1] 1
>
> [[2]]
> [[2]][[1]]
> [1] 3
>
> [[2]][[2]]
> [1] 4
>
>
> [[3]]
> [1] 5
>
>
> But x[[2]][[2]] has been deleted.
>
> Many thanks
>
> Regards,
> David
>
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> and provide commented, minimal, self-contained, reproducible code.
>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901