On 27/07/2012 23:52, Adrian Duşa wrote:
Dear R-devel,
I'm trying to validate the results from a C function, against a (trial
and tested) older R function. For reasons unknown to me, the C
function seems to give different result sometimes at each trial, even
with the very same data.
See the advice in 'Writing R Extensions'. In particular, the most
common cause is the use of initialized values, so run under valgrind.
Also check that your C code does not change any of its arguments: if it
does you may end up with self-modifying R code. (That's probably rare,
but I spent a couple of hours on such an example last night.)
These are the relevant outputs from R:
library(QCA)
Loading required package: lpSolve
benchmark <- function(x, y) {
+ index <- 0
+ while((index <- index + 1) < length(x)) {
+ x <- setdiff(x, findSubsets(y + 1, x[index], max(x)))
+ }
+ return(x)
+ }
set.seed(12345)
exprnec <- sort(sample(13:19683, 500))
noflevels <- rep(2, 9)
mbase <- rev(c(1, cumprod(rev(noflevels + 1))))[-1]
foo1 <- benchmark(exprnec, noflevels)
foo2 <- .Call("removeRedundants", exprnec, noflevels, mbase)
all.equal(foo1, foo2)
[1] "Numeric: lengths (184, 181) differ"
set.seed(12345)
exprnec <- sort(sample(13:19683, 500))
foo2 <- .Call("removeRedundants", exprnec, noflevels, mbase)
all.equal(foo1, foo2)
[1] TRUE
set.seed(12345)
exprnec <- sort(sample(13:19683, 500))
foo2 <- .Call("removeRedundants", exprnec, noflevels, mbase)
all.equal(foo1, foo2)
[1] TRUE
set.seed(12345)
exprnec <- sort(sample(13:19683, 500))
foo2 <- .Call("removeRedundants", exprnec, noflevels, mbase)
all.equal(foo1, foo2)
[1] "Numeric: lengths (184, 173) differ"
The relevant C code can be found here:
http://codeviewer.org/view/code:287e
As I am too baffled by these (to me strange) results, any hint is much
appreciated.
Thanks very much in advance,
Adrian
--
Brian D. Ripley, [email protected]
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
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