[R] aggregate over x cases

[baptiste auguie]

good point, i forgot about head (!),

library(plyr)
ddply(d, .(block, trial), head, 2)

   block trial   x   y
1     1     1 605 150
2     1     1 603 148
3     1     2 607 148
4     1     2 605 152


On 11 May 2009, at 14:04, Gabor Grothendieck wrote:

> 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
>>
>> ______________________________________________
>> 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.
>>
>>
>
> ______________________________________________
> 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.

_____________________________

Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag