[R] Collapsing across trials

[Gabor Grothendieck]

Try

aggregate(DF[4], DF[1:3], mean)


On 12/16/06, Pedro Alcocer <pealco at gmail.com> wrote:
> Hello,
>
> My ultimate goal is a repeated measures (mixed model) ANOVA, however,
> my present question is about how to reorganize my data into the format
> that the ANOVA commands expect. In particular, how to collapse across
> trials. (I am using the tutorial at
> [http://personality-project.org/r/r.anova.html] for the mixed model
> ANOVA)
>
> The data I am using looks like this. A subject sees 10 trials per
> condition and there are 2 conditions. I want the average of all the
> reaction times (RTs) from a subject looking a one condition. I also
> want to retain List in the final output.
>
> Subj    List    Condition       RT
> 2       1       C               338
> 2       1       C               227
> 2       1       C               430
> 2       1       C               621
> 2       1       C               255
> 2       1       C               348
> 2       1       C               280
> 2       1       C               356
> 2       1       C               272
> 2       1       C               346
> 3       2       C               489
> 3       2       C               426
> 3       2       C               352
> 3       2       C               351
> 3       2       C               349
> 3       2       C               403
> 3       2       C               336
> 3       2       C               278
> 3       2       C               365
> 3       2       C               271
> 2       1       D               360
> 2       1       D               374
> 2       1       D               326
> 2       1       D               363
> 2       1       D               290
> 2       1       D               458
> 2       1       D               295
> 2       1       D               362
> 2       1       D               285
> 2       1       D               277
> 3       2       D               354
> 3       2       D               352
> 3       2       D               362
> 3       2       D               360
> 3       2       D               334
> 3       2       D               365
> 3       2       D               335
> 3       2       D               391
> 3       2       D               272
> 3       2       D               618
>
> The result should look like this:
> 2       1       C               (AVG)
> 3       2       C               (AVG)
> 2       1       D               (AVG)
> 3       2       D               (AVG)
>
> Where (AVG) is the average of the 10 trials.
>
> The above is a simplified case. How can I do this with multiple RT
> measurements per subject? In other words, the above, but with more
> than one RT column per subject.
>
> Resulting in:
>
> Subj    List    Condition       RT1             RT2             RT3             RT4             RT5
> 2       1       C               (AVG1)  (AVG2)  (AVG2)  (AVG2)  (AVG2)
> 3       2       C               (AVG1)  (AVG2)  (AVG2)  (AVG2)  (AVG2)
> 2       1       D               (AVG1)  (AVG2)  (AVG2)  (AVG2)  (AVG2)
> 3       2       D               (AVG1)  (AVG2)  (AVG2)  (AVG2)  (AVG2)
>
> I've come across the apply and aggregate functions in online
> documentation, and I have the suspicion that they may be called for
> here, but their application isn't clear to me. I am fairly new to R.
>
> (I am using R 2.4.0 on Mac OS X.)
>
> I'd appreciate any insights.
>
> Pedro Alcocer
> University of Florida
>
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