Vector size limit for table() in R-2.15.1

As the posting guide asked you to before posting, try R-patched.  That has the NEWS items

   ? duplicated(), unique() and similar now support vectors of
     lengths above 2^29 on 64-bit platforms.

   ? unique() and similar would infinite-loop if called on a vector of
     length > 2^29 (but reported that the vector was too long for 2^30
     or more).

If you want to work on such large datasets, you might want to consider using R-devel which has a number of enhancements already with more in the pipeline.

On 10/08/2012 01:29, Sean Ruddy wrote:

Hi,

First, thanks in advance. Some useful info:

version

platform       x86_64-unknown-linux-gnu
arch           x86_64
os             linux-gnu
system         x86_64, linux-gnu
version.string R version 2.15.1 (2012-06-22)

I'm trying to use the table() function on a 2 column matrix that has 711
million rows (see below). However, it freezes. If I subset the matrix to be
less than or equal to 2^29 (500+ million) then the table() function
finishes in minutes. As soon as I go larger than that--beginning with
2^29+1--it gets stuck, ie. nothing happens even after hours of running. I
assume it has something to do with memory since I believe that's the 32 bit
limit but I'm running on a 64 bit machine.

Here's the matrix:

head(DRI.mtx)

  POSITION BP
 38076904  C
 38076905  C
 38076906  A
 38076907  T
 38076908  C
 38076909  C


The result from table (if the matrix has less than 2^29 rows) is

head(table(DRI.mtx))

                  BP
POSITION     A C  G N  T
  115247036 17 0  0 0  0
  115247037 31 0  0 0  0
  115247038 46 0  0 0  0
  115247039  0 0 54 0  0
  115247040  0 0  1 0 66
  115247041  0 0  0 0 78


I've tracked the problem down to the C-file, "unique.c". table() calls
factor() which calls unique() which I believe calls "unique.c". Browsing
through the C file I found an if statement that checks if the size of the
vector is larger than 2^30-1. If TRUE it gives the error message "too large
for hashing". I do not get any error message when I run table() on the full
matrix but I wonder if maybe I should be and if the limit of 2^30 is too
high and should be lowered. Maybe it's just my set up or maybe it has
nothing to do with unique.c. I don't know.

Here's the part of unique.c I was referring to:

/*
  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 <= 2^30.

  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 n2 = 2 * n;
    if(n < 0 || n > 1073741824) /* protect against overflow to -ve */
        error(_("length %d is too large for hashing"), n);
    d->M = 2;
    d->K = 1;
    while (d->M < n2) {
        d->M *= 2;
        d->K += 1;
    }
}

"n" I presume is the number of rows of the matrix so I don't see why this
wouldn't run properly though I'm not sure what is causing the problem in
the unique.c file and I have no idea how to troubleshoot.

I have a work around that reads in chunks at a time, but I'm very
interested in why there appears to be a limit at 2^29 when according to the
unique.c file it should be twice that.

Thanks for the help.

-Sean

   [[alternative HTML version deleted]]

-- 
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