On Mon, 17 Oct 2011, Brian Smith wrote:
Hi,
I had a large file for which I require a subset of rows. Instead of reading
it all into memory, I use the awk command to get the relevant rows. However,
I'm doing it pretty inefficiently as I write the subset to disk, before
reading it into R. Is there a way that I can read it into an R object
without writing to disk? For example, this is what I do currently:
## write test sample file
mat1 <- matrix(sample(1:100,16),8,2)
fname1 <- 'temp1.txt'
fname2 <- 'temp2.txt'
write.table(mat1,fname1,sep='\t',row.names=F,col.names=F)
## Read a subset of rows, write to file, and read from file
system(paste("awk '(NR > 1 && NR < 4) {print $0}' ",fname1," >
",fname2,sep=''))
mat2 <- read.table(fname2,sep='\t')
print(mat2)
#####
Is there a way that I can skip writing to disk?
Use a pipe() connection.
thanks!
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Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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