[R] aggregate over x cases

[Gabor Grothendieck]

Try this:

do.call(rbind, by(DF, DF[1:2], head, 2))

On Mon, May 11, 2009 at 7:49 AM, Jens Bölte <boelte at 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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