Here is a way of doing it:
> x
block trial x y
1 1 1 605 150
2 1 1 603 148
3 1 1 604 140
4 1 1 600 140
5 1 1 590 135
6 1 1 580 135
7 1 2 607 148
8 1 2 605 152
10 1 2 600 158
> do.call(rbind, lapply(split(x, list(x$block, x$trial), drop=TRUE), head,
2))
block trial x y
1.1.1 1 1 605 150
1.1.2 1 1 603 148
1.2.7 1 2 607 148
1.2.8 1 2 605 152
On Mon, May 11, 2009 at 7:49 AM, Jens Bölte <boe...@psy.uni-muenster.de>wrote:
> Hello,
>
> I have been struggling for quite some time to find a solution for the
> following problem. I have a data frame which is organized by block and
> trial. Each trial is represented across several rows in this data frame. I'd
> like to extract the first x rows per trial and block.
>
> For example
> block trial x y
> 1 1 1 605 150
> 2 1 1 603 148
> 3 1 1 604 140
> 4 1 1 600 140
> 5 1 1 590 135
> 6 1 1 580 135
> 7 1 2 607 148
> 8 1 2 605 152
> 10 1 2 600 158
> .....
>
> Selecting only the the first two rows per trial should result in
> block trial x y 1 1 605 150
> 1 1 603 148
> 1 2 607 148
> 1 2 605 152
>
> The data I am dealing with a x-y coordinates (samples) from an eye-tracking
> experiment. I receive the data in this format and need to eliminate unwanted
> samples.
>
> Thanks Jens Bölte
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html<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 that you are trying to solve?
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