[R] How to import specific column(s) using "read.table"?
Prof Brian Ripley
ripley at stats.ox.ac.uk
Mon Aug 9 22:56:42 CEST 2004
There is no way for read.table to skip columns. It is however very easy
to do this with a preprocessing of the table: cut, awk and perl all come
to mind, and you could do it in R too, reading a block of rows at a time
and writing them back out.
scan() can skip columns, but I would still use preprocessing with scan.
On Mon, 9 Aug 2004, F Duan wrote:
> I have a very big tab-delim txt file with header and I only want to import
> several columns into R. I checked the options for "read.table" and only
> found "nrows" which lets you specify the maximum number of rows to read in.
> Although I can use some text editors (e.g., wordpad) to edit the txt file first
> before running R, I feel its not very convenient. The reason for me to do this
> is that if I import the whole file into R, it will eat up too much of my
> systems memory. Even after I remove it later, I still cant release the memory.
The peculiar quotes suggest this is Windows -- the Rtools we use to build
R there contain a cut.exe.
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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