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

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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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