unique possible bug

Hi,

I am trying to read in a rather large list of transactions using the
arules library.

It seems in the coerce method into the dgCmatrix, it
somewhere calls unique. Unique.c throws an error when  n>  536870912;
however, when 4*n was modified to 2*n in 2004, the overflow protection
should have changed from 2^29 to 2^30, right? If so, how would I
change it in my copy? Do I have to recompile everything?

Thanks,
Patrick McCann


Here is a simple to reproduce example:

runif(2^29+5)->a
sum(unique(a))->b

Error in unique.default(a) : length 536870917 is too large for hashing

traceback()

3: unique.default(a)
2: unique(a)
1: unique(a)

unique.default

function (x, incomparables = FALSE, fromLast = FALSE, ...)
{
     z<- .Internal(unique(x, incomparables, fromLast))
     if (is.factor(x))
         factor(z, levels = seq_len(nlevels(x)), labels = levels(x),
             ordered = is.ordered(x))
     else if (inherits(x, "POSIXct"))
         structure(z, class = class(x), tzone = attr(x, "tzone"))
     else if (inherits(x, "Date"))
         structure(z, class = class(x))
     else z
}
<environment: namespace:base>

From http://svn.r-project.org/R/trunk/src/main/unique.c I see:

/*
  Choose M to be the smallest power of 2
  not less than 2*n and set K = log2(M).
  Need K>= 1 and hence M>= 2, and 2^M<= 2^31 -1, hence n<= 2^29.

  Dec 2004: modified from 4*n to 2*n, since in the worst case we have
  a 50% full table, and that is still rather efficient -- see
  R. Sedgewick (1998) Algorithms in C++ 3rd edition p.606.
*/
static void MKsetup(int n, HashData *d)
{
    int n4 = 2 * n;

    if(n<  0 || n>  536870912) /* protect against overflow to -ve */
        error(_("length %d is too large for hashing"), n);
    d->M = 2;
    d->K = 1;
    while (d->M<  n4) {
        d->M *= 2;
        d->K += 1;
    }
}