[R] Strange behaviour using .Fortran

[Uli Flenker; Raum 704]

Hello everybody,

I observed some strange behaviour of R (0.64.1/Linux 2.0.25) when trying
to use FORTRAN-libraries.

I first downloaded "ALGORITHM AS 304" from StatLib. All I changed  at
the code, was to substitute "REAL"-routines by "DOUBLE PRECISION".

Compiling went o.k.:

> g77 -fpic -O2 -shared -o rtest.o fisher.f

 ("g77 --version" gives 2.7.2.1)


Here are the first lines of the code from AS 304, "FISHER" being the
routine to be used from within R:

      SUBROUTINE FISHER (X, M, Y, N, TOTAL, POSSIB, P, IFAULT)
C
C        ALGORITHM AS 304.1 APPL.STATIST. (1996), VOL.45, NO.3
C
C        Fisher's non-parametric randomization test for two small
C        independent random samples
C
      INTEGER M, N, TOTAL, POSSIB, IFAULT
      DOUBLE PRECISION X(*), Y(*), P

C
	... etc., lots of code ...



Here is the prototype of R-code that I used ...


> dyn.load("/path-to-lib/rtest.o")

> fisher.ts.test<-function(x,y){

   nx<-length(x)
   ny<-length(y)

         
   ftr..out<-.Fortran("fisher",
                     as.real(x),
                     as.integer(nx),
                     as.real(y),
                     as.integer(ny),
                     as.integer(0),
                     as.integer(0),
                     as.real(0.0),
                     as.integer(0))

return(ftr.out)
}


Loading the code was no Problem. Now, here is what I obtained when using
it:

> a<-c(18,19,25)
> b<-c(20,29,29,30,31,31,31)

> fisher.ts.test(x,y)
[[1]]
[1] 18 19 25

[[2]]
[1] 3

[[3]]
[1] 20 29 29 30 31 31 31

[[4]]
[1] 7

[[5]]
[1] 1

[[6]]
[1] 120

[[7]]
[1] 0.01666667

[[8]]
[1] 0

.. which are the correct results.


But invoking it exchanging "a" and "b" gives the following weird result:

> tse.test(b,a)
[[1]]
[1] 31 31 31 30 31 31 31

[[2]]
[1] 3

[[3]]
[1] 20 29 29

[[4]]
[1] 0

[[5]]
[1] 0

[[6]]
[1] 1

[[7]]
[1] 1

[[8]]
[1] 0


This could not be observed when using a similar routine written in
Xlisp-Stat. A small FORTRAN-Program that allowed to type in the data
interactively also didn't care about the order of the size or sum of the
samples, which makes me conclude the reason is somewhere in R.

Any ideas?


If the problem is very obvious, please have mercy with a pure user of R,
who makes his first attempts to dig a little deeper ... 

        Uli Flenker
        Institute of Biochemistry
        German Sports University Cologne
        Carl-Diem-Weg 6

        50933 Cologne/Germany

        Phone: 0049/0221/4982-493
                             -494

 



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