grep lines before or after pattern matched?

Mon, Jul 11, 2011 11:19 AM

Try this (untested as I'm on my iPhone now):

index <- grep("Document+.", yourfile, value = FALSE)
index <- c(index + 2, index + 4)

You just need to make sure you avoid recycling, e.g.,

1:10 + c(2, 4) # not what you want

If you want a sufficient number of lines that manually writing index + becomes cumbersome, you could use something like:

as.vector(sapply(c(2, 4), "+", e2 = index))

HTH,

Josh

On Jul 11, 2011, at 11:09, Simon Kiss <sjkiss at gmail.com> wrote:

Josh, that's amazing. Is there any way to have it grab two different lines after the grep, say the second and the fourth line? There's some other information in the text file I'd like to grab.  I could do two separate commands, but I'd like to know if this could be done in one command...
Simon Kiss
On 2011-07-11, at 1:31 PM, Joshua Wiley wrote:

If you know you can find the start of the document (say that line
always starts with Document...), then:

grep("Document+.", yourfile, value = FALSE) + 4

should give you 4 lines after each line where Document occurred.  No
loop needed :)

On Mon, Jul 11, 2011 at 10:25 AM, Simon Kiss <sjkiss at gmail.com> wrote:

Hi Josh,
Sorry for the insufficient introduction. This might work, but I'm not sure.
The file that I have includes up to 100 documents (Document 1, Document 2, Document 3....Document 100) with the newspaper name following 4 lines below each Document number.
I'm using readlines to get the text file into R and then trying to use grep to get the newspaper name for each record. But your idea of indexing the text object read into R with the line number where the newspaper name is found is a good one.  I'll just have to come up with a loop to tell R to get the 4th, 8th, 12, 16th, line, etc.
I'll see if I can get that to work.
Simon
On 2011-07-11, at 12:45 PM, Joshua Wiley wrote:

Dear Simon,

Maybe I don't understand properly....if you are doing this in R, can't
you just pick the line you want?

Josh

## print your data to clipboard
cat("Document 1 of 100 \n \n \n Newspaper Name \n \n Day Date", file =
"clipboard")
## read data in, and only select the 4th line to pass to grep()
grep("pattern", x = readLines("clipboard")[4])


On Mon, Jul 11, 2011 at 9:31 AM, Simon Kiss <sjkiss at gmail.com> wrote:

Dear colleagues,
I have a series of newspaper articles in a text file, downloaded from a text file.  They look as follows:

Document 1 of 100
\n
\n
\n
Newspaper Name
\n
\n
Day Date

I have a series of grep scripts that can extract the date and convert it to a date object, but I can't figure out how to grep the newspaper name.  There is no field ID attached to those lines. The best I can come up with would be to have the program grep the four lines following matching the pattern "Document [0-9]".  There is an an argument to grep in unix that can do this ...grep -A4 'pattern' infile>outfile, but I don't know if there is an equivalent argument in R.

Any thoughts.
Yours, Simon Kiss
*********************************
Simon J. Kiss, PhD
Assistant Professor, Wilfrid Laurier University
73 George Street
Brantford, Ontario, Canada
N3T 2C9
Cell: +1 905 746 7606

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grep lines before or after pattern matched?

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