[R] Vector size limit for table() in R-2.15.1

[Prof Brian Ripley]

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]]
>
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>


-- 
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