R help - Aug 2007 - Possible memory leak with large matrices in R v.2.5.0

I'm working with a very large matrix ( 22k rows x 2k cols) of RNA 
expression data with R v.2.5.0 on a RedHat Enterprise machine, x86_64 
architecture.

The relevant code is below, but I call a function that takes a cluster 
of this data ( a list structure that contains a $rows elt which lists 
the rows (genes ) in the cluster by ID, but not the actual data itself ).

The function creates two copies of the matrix, one containing the rows 
in the cluster, and one with the rest of the rows in the matrix.  After 
doing some statistical massaging, the function returns a statistical 
score for each rows/genes in the matrix, producing a vector of 22k elt's.

When I run 'top', I see that the memory stamp of R after loading the 
matrix is ~750M.  However, after calling this function on 10 clusters, 
this jumps to > 3.7 gig (at least by 'top's measurement), and this
will
not be reduced by any subsequent calls to gc().

Output from gc() is:

     > gc()           used  (Mb) gc trigger   (Mb) max used  (Mb)
    Ncells   377925  20.2    6819934  364.3   604878  32.4
    Vcells 88857341 678.0  240204174 1832.7 90689707 692.0
     >

output from top is:

      PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
     1199 waltman   17   0 3844m 3.7g 3216 S  0.0 23.6  29:58.74 R

Note, the relevant call that invoked my function is:

    test <- sapply( c(1:10), function(x) get.vars.for.cluster(
    clusterStack[[x]], opt="rows" ) )

Finally, for fun, I rm()'d all variables with the rm( list=ls() ) 
command, and then called gc().  The memory of this "empty" instance of
R
is still 3.4 gig, i.e.

R.console:

     > rm( list=ls() )
     > ls()
    character(0)
     > gc()
               used  (Mb) gc trigger   (Mb) max used  (Mb)
    Ncells   363023  19.4    5455947  291.4   604878  32.4
    Vcells 44434871 339.1  192163339 1466.1 90689707 692.0
     >

Subsequent top  output:
output from top is:

      PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
     1199 waltman   16   0 3507m 3.4g 3216 S  0.0 21.5  29:58.92 R  


Thanks for any help or suggestions,

Peter Waltman

p.s.  code snippet follows.  Note, that I've added extra rm() and gc() 
calls w/in the function to try to reduce the memory stamp to no avail.

        get.vars.for.cluster = function( cluster,
                                         genes=get.global( "gene.ids"
),
                                        
opt=c("rows","cols"),
                                         ratios=get.global("ratios"),
                                         var.norm=T,
                                         r.sig=get.global( "r.sig" ),
                                         allow.anticor=get.global(
    "allow.anticor" ) ) {
          cluster <<- cluster

          opt <- match.arg( opt )
          rows <- cluster$rows
          cols <- cluster$cols

          if ( opt == "rows" ) {
            r <- ratios[ rows, cols ]
            r.all <- ratios[ genes, cols ]

            avg.rows <- apply( r, 2, mean, na.rm=T ) ##median )

            rm( r ) 
            gc()

            devs <- apply( r.all, 1, "-", avg.rows )

            if ( !allow.anticor ) {
              rm( r.all, avg.rows ) 
              gc()
            }

            vars <- apply( devs, 2, var, na.rm=T )

            rm( devs )
            gc()

            vars <- log10( vars )
            gc()

            if ( allow.anticor ) {
              ## Get variance against the inverse of the mean profile
              devs.2 <- apply( r.all, 1, "-", -avg.rows )
              gc()

              vars.2 <- apply( devs.2, 2, var, na.rm=T )
              gc()

              rm( devs.2 )
              gc()

              vars.2 <- log10( vars.2 )
              gc()

               ## For each gene take the min of variance or anti-cor
    variance
              vars <- cbind( vars, vars.2 )

              rm( vars.2 )
              gc()

              vars <- apply( vars, 1, min )
              gc()

            }

                ## Normalize the values by the variance over the rows in
    the cluster
            if ( var.norm ) {

              vars <- vars - mean( vars[ rows ], na.rm=T )
              tmp.sd <- sd( vars[ rows ], na.rm=T )
              if ( ! is.na( tmp.sd ) && tmp.sd != 0 ) vars <- vars /
(
    tmp.sd + r.sig )
            }
            gc()
            return( vars )

          } else {

            r.all <- ratios[ rows, ]
            ## Mean-normalized variance
            vars <- log10( apply( r.all, 2, var, na.rm=T ) / abs( apply(
    r.all, 2, mean, na.rm=T ) ) )
            names( vars ) <- colnames( ratios )

            ## Normalize the values by the variance over the rows in the
    cluster
            if ( var.norm ) {
              vars <- vars - mean( vars[ cluster$cols ], na.rm=T )
              tmp.sd <- sd( vars[ cluster$cols ], na.rm=T )
              if ( ! is.na( tmp.sd ) && tmp.sd != 0 ) vars <- vars /
(
    tmp.sd + r.sig )
            }

            return( vars )
          }
        }