Le 16/11/12 14:00, Hadley Wickham a écrit :
On Fri, Nov 16, 2012 at 2:25 AM, Romain Francois
<[email protected]> wrote:
Thanks for exploring these issue. This looks very useful.
I get:
str( first_log(NA) )
logi TRUE
str( first_int(NA_integer_) )
int NA
str( first_num(NA_real_) )
num NA
str( first_char(NA_character_) )
chr "NA"
For first_log: a bool can either be true or false. In R logical vectors are
represented as arrays of ints. When we coerce to bool, we test whether the
value is not 0. This works for most cases. I guess conversion to bool should
be avoided.
There's obviously no perfect solution, and that seems to be consistent
with C++'s treatment of NAs in logical expression: evalCpp("NAN ||
FALSE") == TRUE
We have the is_na template function that can help:
evalCpp( 'traits::is_na<LGLSXP>( NA_LOGICAL )' )
[1] TRUE
evalCpp( 'traits::is_na<REALSXP>( NA_REAL )' )
[1] TRUE
And from this I can see we don't have is_na<STRSXP>, will fix this.
str( evalCpp( 'traits::get_na<REALSXP>()' ) )
num NA
str( evalCpp( 'traits::get_na<INTSXP>()' ) )
int NA
I guess we could come up with a nicer syntax for these, maybe static
functions in Vector<> so that we could do :
IntegerVector::is_na( )
NumericVector::get_na( )
Yes, that would be very nice.
Done.
str( evalCpp( 'std::numeric_limits<int>::min()' ) )
int NA
This is how NA_integer_ is represented.
Thanks - the danger is that you might do something like:
evalCpp( 'traits::get_na<INTSXP>() + 1' )
I'll make a note.
Yes. NA are particularly annoying in integer vector.
As said above, I'll add
...Vector::is_na
...Vector::get_na
to have something more consistent and not as cryptic as traits::is_na<...>(
). People should not need to know what REALSXP, INTSXP, LGLSXP, ... mean.
Great, thanks!
Hadley
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