[R] Strange integer result on Debian/amd64

[Dave Ewart]

On Wednesday, 21.03.2007 at 14:07 +0800, Berwin A Turlach wrote:

> > All help/suggestions/appreciated!
> 
> The calculations are done in floating point arithmetic, not integer
> arithmetic. From the help page on `choose' one might already guess
> so much, but reading "R-2.4.1/src/nmath/choose.c" definitely confirms
> this fact.
> 
> Thus, your problem is covered by FAQ 7.31:
> 
> http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f

Thanks Berwin.

OK, I understand the problem now.  I was wondering if it something along
those lines, but initially dismissed that as a possibility since I
expected 'choose' to be an integer calculation. 

However, the underlying problem that gave rise to the difficulty was as
follows.  A colleague wishes to create a matrix, where one of the
dimensions of the matrix is the result of the 'choose' function, i.e.

  mycols<-choose(11,6)
  a_matrix<-matrix(0,nrow=11,ncol=mycols)

Clearly, 'ncol' casts mycols as as integer.  In this case, a_matrix has
only 461 columns, not 462.

What's the best way to make this work as required?

Dave.
-- 
Dave Ewart
davee at ceu.ox.ac.uk
Computing Manager, Cancer Epidemiology Unit
Cancer Research UK / Oxford University
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Get key from http://www.ceu.ox.ac.uk/~davee/davee-ceu-ox-ac-uk.asc
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