Hi Jim,

Here is a suggestion using aggregate():

res <- with(df, aggregate(Angle, list(Trial, Treatment), mean, na.rm =
TRUE))
colnames(res) <- c('Trial','Treatment', 'Average_Angle')
res
# Trial Treatment Average_Angle
# 1     1         C       52.7455
# 2     2         C       81.7599
# 3     3         C       76.3234
# 4     1         U       62.5118
# 5     2         U       81.5520

HTH,
Jorge


On Thu, Nov 5, 2009 at 8:53 PM, jimdare <> wrote:

>
> Hi,
>
> I am create a new DF that summarizes the mean angle per treatment/trial, of
> the original DF (see below).  I have had some success using:
> (tapply(df$Angle, INDEX=interaction(df$State,
> df$Trial),  FUN=mean)); however, this gives the answer as a list, which
> means I would have to split the name to get the categories back.  Does
> anyone know a simple way to transform the Original DF into Summary DF?
>
> Thanks in advance,
>
> James
>
>
> Original DF
>
> > df
>       Angle Trial    Treatment
> 1    43.1297     1   C
> 2    62.3613     1   C
> 3    88.2767     2   C
> 4    75.2431     2   C
> 5    91.3668     3   C
> 6    61.2800     3   C
> 7    55.5575     1   U
> 8    69.4661     1   U
> 9    67.5512     2   U
> 10   95.5528     2   U
> 11   75.8689     3   U
> 12   66.9070     3   U
>
> Summary DF
>
> > sdf
>
>       Angle Trial    Treatment
> 1    52.7455   1   C
> 2    ...           2   C
> 3    ...           3   C
> 4    ...           1   U
> 5    ...           2   U
> 6    ...           3   U
>
> --
> View this message in context:
> http://old.nabble.com/Calculate-Mean-for-each-Treatment-Trial-Interaction-in-DF-tp26225533p26225533.html
> Sent from the R help mailing list archive at Nabble.com.
>
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