On Mon, 4 Apr 2011, Andrew Yee wrote:
This has to do with using pipe() and grep and read.csv()
I have a .csv file that I grep using pipe() and read.csv() as follows:
read.csv(pipe('grep foo bar.csv'))
However, is there a way to have this command run when for example,
there is no "foo" text in the bar.csv file? I get an error message
(appropriately):
Error in read.table(file = file, header = header, sep = sep, quote = quote, :
no lines available in input
Is there a way to "inspect" the output of pipe before passing it on to
read.csv()?
You have to read from a pipe to 'inspect' it. So
tmp <- readLines(pipe('grep foo bar.csv'))
if(!length(tmp)) do something else
else {
res <- read.csv(con <- textConnection(tmp))
close(con)
}
OTOH, unless the file is enormous you could simply read it into R and
use grep(value = TRUE) on the character vector.
Thanks,
Andrew
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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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Oxford OX1 3TG, UK Fax: +44 1865 272595
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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