Scanning data files line-by-line

4 messages · R A F, Brian Ripley, Duncan Murdoch

Original

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R A F

Wed, Apr 30, 2003 5:45 AM #

Maybe I'm missing something.  When I do readLines( "file", n = 1) and
repeat, it always reads the first line of "file".  I've to be able to
advance to the next line, no?

I'll take a look at the command file(), as someone else suggested.

Thanks.

Brian Ripley

Wed, Apr 30, 2003 6:13 AM #

On Wed, 30 Apr 2003, R A F wrote:

You need to open the connection first.  readLines( "file", n = 1)
opens file "file", reads a line and then closes "file".  It has no idea
that you want to keep reading the same file.

It's open() you need, as in

con <- file("file")
open(con)
for(i in 1:10) print(readLines(con, n=1))
close(con)

In C you would need to (f)open a file to read it line-by-line, just as 
here.

The first two lines can be collapsed to

con <- file("file", "r")

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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)
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Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Wed, Apr 30, 2003 6:19 AM #

On Wed, 30 Apr 2003 12:45:33 +0000, RAF wrote:

Yes, that's your solution.  

con <- file("foo") 

will open the file called foo and attach it to a connection called
con.  You pass con to readLines, and since the file stays open between
calls, you'll get successive lines.  Remember close(con) when you're
done.

Duncan Murdoch

Wed, Apr 30, 2003 7:55 AM #

On Wed, 30 Apr 2003 09:19:20 -0400, I wrote:

Whoops, believe Brian, not me.  You need 

 con <- file("file", "r")

Duncan Murdoch