[Rd] R's IO speed

Prof Brian Ripley ripley at stats.ox.ac.uk
Sun Dec 26 11:03:30 CET 2004

R-devel now has some improved versions of read.table and write.table.

For a million-row data frame containing one number, one factor with few 
levels and one logical column, a 56Mb object.

generating it takes 4.5 secs.

calling summary() on it takes 2.2 secs.

writing it takes 8 secs and an additional 10Mb.

saving it in .rda format takes 4 secs.

reading it naively takes 28 secs and an additional 240Mb

reading it carefully (using nrows, colClasses and comment.char) takes 16 
secs and an additional 150Mb (56Mb of which is for the object read in).
(The overhead of read.table over scan was about 2 secs, mainly in the 
conversion back to a factor.)

loading from .rda format takes 3.4 secs.

[R 2.0.1 read in 23 secs using an additional 210Mb, and wrote in 50 secs 
using an additional 450Mb.]

Will Frank Harrell or someone else please explain to me a real application 
in which this is not fast enough?

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

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