Hi the list,
I am writing a R function that call a C function. The C function needs
integers but I do not manage to give a NA integer as argument :
--- C code ---
void essai(int *t){
Rprintf("\nT0=%i T1=%i T2=%i T3=%i",t[0],t[1],t[2],t[3]);
}
--- R ---
boub <- c(1,2,3,4)
.C("pour",as.integer(boub),NAOK=TRUE)
# T0=1 T1=2 T2=3 T3=4[[1]]
# [1] 1 2 3 4
boub <- c(1,2,NA,4)
.C("essai",as.integer(boub),NAOK=TRUE)
# T0=1 T1=2 T2=-2147483648 T3=4[[1]]
# [1] 1 2 NA 4
--- ---
In the second example, T2=-2147483648 and not NA.
I check the "writing R extension", there is a part that explain that the
test of NA is not the same between double and integer (NA_INTEGER,
ISNA), but I did not find explanation on passing NA argument as integer.
Any idea of what is wrong in my code?
Christophe
Argument as.integer(NA) to a function C
3 messages · Christophe Genolini, Simon Urbanek, Brian Ripley
On Jun 18, 2009, at 9:57 , Christophe Genolini wrote:
Hi the list,
I am writing a R function that call a C function. The C function
needs integers but I do not manage to give a NA integer as argument :
--- C code ---
void essai(int *t){
Rprintf("\nT0=%i T1=%i T2=%i T3=%i",t[0],t[1],t[2],t[3]);
}
--- R ---
boub <- c(1,2,3,4)
.C("pour",as.integer(boub),NAOK=TRUE)
# T0=1 T1=2 T2=3 T3=4[[1]]
# [1] 1 2 3 4
boub <- c(1,2,NA,4)
.C("essai",as.integer(boub),NAOK=TRUE)
# T0=1 T1=2 T2=-2147483648 T3=4[[1]]
# [1] 1 2 NA 4
--- ---
In the second example, T2=-2147483648 and not NA.
I check the "writing R extension", there is a part that explain that
the test of NA is not the same between double and integer
(NA_INTEGER, ISNA), but I did not find explanation on passing NA
argument as integer.
Any idea of what is wrong in my code?
I don't see any problem - in C there is no inherent NA, so what you get is NA_INTEGER value which prints as -2147483648 when you print it as integer (which is what you do in essai). Cheers, S
On Thu, 18 Jun 2009, Christophe Genolini wrote:
Hi the list,
I am writing a R function that call a C function. The C function needs
integers but I do not manage to give a NA integer as argument :
--- C code ---
void essai(int *t){
Rprintf("\nT0=%i T1=%i T2=%i T3=%i",t[0],t[1],t[2],t[3]);
}
--- R ---
boub <- c(1,2,3,4)
.C("pour",as.integer(boub),NAOK=TRUE)
# T0=1 T1=2 T2=3 T3=4[[1]]
# [1] 1 2 3 4
boub <- c(1,2,NA,4)
.C("essai",as.integer(boub),NAOK=TRUE)
# T0=1 T1=2 T2=-2147483648 T3=4[[1]]
# [1] 1 2 NA 4
--- ---
In the second example, T2=-2147483648 and not NA.
I check the "writing R extension", there is a part that explain that the test
of NA is not the same between double and integer (NA_INTEGER, ISNA), but I
did not find explanation on passing NA argument as integer.
Any idea of what is wrong in my code?
Simple: Rprintf does not know about NAs (and nor does printf). From the manual: The most useful function for printing from a C routine compiled into R is Rprintf. This is used in exactly the same way as printf, but is guaranteed to write to R's output (which might be a GUI console rather than a file). The value of NA is stored as NA_INTEGER = -2^32, and if you want your C code to be aware of it, *you* need to program so that value is treated specially. (Since double NAs are stored as a particular NaN, the default C handling of doubles will probably do something sensible but careful code will also need to take the difference between NaNs into account.)
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595