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

From: Charles C. Berry <cberry_at_tajo.ucsd.edu>
Date: Mon, 3 Dec 2007 13:10:39 -0800

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
>
> ______________________________________________
> R-help_at_r-project.org mailing list
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>

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

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