R help - May 2009 - aggregate over x cases

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 B?lte

try this,


library(plyr)
ddply(d, .(block, trial), function(.d) .d[1:2, ])
>   block trial   x   y
> 1     1     1 605 150
> 2     1     1 603 148
> 3     1     2 607 148
> 4     1     2 605 152
HTH,

baptiste


On 11 May 2009, at 13:49, Jens B?lte 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 B?lte
> <ATT00001.txt>
_____________________________

Baptiste Augui?

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

Phone: +44 1392 264187

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

Try this:

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

On Mon, May 11, 2009 at 7:49 AM, Jens B?lte <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 B?lte
>
> ______________________________________________
> 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.
>
>

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
<boelte@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@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<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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