[R] Suggestion for big files [was: Re: A comment about R:]

[ronggui]

2006/1/6, jim holtman <jholtman at gmail.com>:
> If what you are reading in is numeric data, then it would require (807 *
> 118519 * 8) 760MB just to store a single copy of the object -- more memory
> than you have on your computer.  If you were reading it in, then the problem
> is the paging that was occurring.
In fact,If I read it in 3 pieces, each is about 170M.

>
> You have to look at storing this in a database and working on a subset of
> the data.  Do you really need to have all 807 variables in memory at the
> same time?

Yip,I don't need all the variables.But I don't know how to get the
necessary  variables into R.

At last I  read the data in piece and use RSQLite package to write it
to a database.and do then do the analysis. If i am familiar with
database software, using database (and R) is the best choice,but
convert the file into database format is not an easy job for me.I ask
for help in SQLite list,but the solution is not satisfying as that
required the knowledge about the third script language.After searching
the internet,I get this solution:

#begin
rm(list=ls())
f<-file("D:\wvsevs_sb_v4.csv","r")
i <- 0
done <- FALSE
library(RSQLite)
con<-dbConnect("SQLite","c:\sqlite\database.db3")
tim1<-Sys.time()

while(!done){
i<-i+1
tt<-readLines(f,2500)
if (length(tt)<2500) done <- TRUE
tt<-textConnection(tt)
if (i==1) {
           assign("dat",read.table(tt,head=T,sep=",",quote=""));
         }
else assign("dat",read.table(tt,head=F,sep=",",quote=""))
close(tt)
ifelse(dbExistsTable(con, "wvs"),dbWriteTable(con,"wvs",dat,append=T),
  dbWriteTable(con,"wvs",dat) )
}
close(f)
#end
It's not the best solution,but it works.



> If you use 'scan', you could specify that you do not want some of the
> variables read in so it might make a more reasonably sized objects.
>
>
> On 1/5/06, FranÃ§ois Pinard <pinard at iro.umontreal.ca> wrote:
> > [ronggui]
> >
> > >R's week when handling large data file.  I has a data file : 807 vars,
> > >118519 obs.and its CVS format.  Stata can read it in in 2 minus,but In
> > >my PC,R almost can not handle. my pc's cpu 1.7G ;RAM 512M.
> >
> > Just (another) thought.  I used to use SPSS, many, many years ago, on
> > CDC machines, where the CPU had limited memory and no kind of paging
> > architecture.  Files did not need to be very large for being too large.
> >
> > SPSS had a feature that was then useful, about the capability of
> > sampling a big dataset directly at file read time, quite before
> > processing starts.  Maybe something similar could help in R (that is,
> > instead of reading the whole data in memory, _then_ sampling it.)
> >
> > One can read records from a file, up to a preset amount of them.  If the
> > file happens to contain more records than that preset number (the number
> > of records in the whole file is not known beforehand), already read
> > records may be dropped at random and replaced by other records coming
> > from the file being read.  If the random selection algorithm is properly
> > chosen, it can be made so that all records in the original file have
> > equal probability of being kept in the final subset.
> >
> > If such a sampling facility was built right within usual R reading
> > routines (triggered by an extra argument, say), it could offer
> > a compromise for processing large files, and also sometimes accelerate
> > computations for big problems, even when memory is not at stake.
> >
> > --
> > FranÃ§ois Pinard   http://pinard.progiciels-bpi.ca
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
> >
>
>
>
> --
> Jim Holtman
> Cincinnati, OH
> +1 513 247 0281
>
> What the problem you are trying to solve?


--
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Deparment of Sociology
Fudan University