[R] skip non-sequential lines using scan?

[jim holtman]

simplest thing is to read in all 100 rows and then just select the
ones you want:

x <- scan(........)
x <- lapply(x, '[', seq(5,99,2))

On Nov 8, 2007 4:19 AM, Matthew Keller <mckellercran at gmail.com> wrote:
> Hi all,
>
> Is there a way to skip non-sequential lines using the "skip" argument
> in the scan function?
>
> E.g., I have a matrix with 100 rows and 1e7 columns. I open a
> connection and want to read only lines 5, 7, 9, etc [i.e.,
> seq(5,99,2)]
>
> It might seem that the syntax to do this would be something like this
> (if only the "skip" allowed vectors in the same way colClasses does in
> read.table):
>
> con <- file("bigfile",open="r")
> rows.I.want <- seq(5,99,2)
> new <- scan(con,what="character",skip=rows.I.want-1,nlines=rows.I.want)
>
> The above doesn't work - it would read lines 5, 6, 7, ...
> length(seq(5,99,2)) rather than 5, 7, 9, ... 99. Yes, I know I can
> accomplish this by looping, but with the huge datasets I'll be working
> with, I'd like to try to save time by doing it all at once. Any ideas?
>
> Matt
>
>
>
> --
> Matthew C Keller
> Asst. Professor of Psychology
> University of Colorado at Boulder
> www.matthewckeller.com
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?