how to handle no lines in input with pipe()

Thank you very much for your suggestion...that works perfectly.

Thanks,
Andrew
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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how to handle no lines in input with pipe()

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