[R] how to calculate the mean of a group in a table

[John Kane]

I see you already have three solutions but, just for the heck of it, here's another. I am trying to get familiar with the reshape2 package and your question was a good exercise for me. 


With your data set named xx:

library(reshape2)

yy <- melt(xx, id=c("period", "treatment", "session",
     "type","stage"), measured=c("wage_accepted"))

dcast(yy, period + stage ~ variable, mean)

As for your request for tutorials for loops and if-else materials, I cannot make any better suggestions than you already have. However, in R, if you are thinking of using these it usually means you are not thinking properly in R.  There are "usually" faster and better was of achieving the desired results in R. Sometimes a loop or if-else is appropriate but usually in many fewer instances than in most other languages.

By the way type is a reserved(? name in R. Not a problem here but it's safer not to use reserved words in R.


--- On Sat, 5/7/11, tornanddesperate <MatthiasNeff at gmx.ch> wrote:

> From: tornanddesperate <MatthiasNeff at gmx.ch>
> Subject: [R] how to calculate the mean of a group in a table
> To: r-help at r-project.org
> Received: Saturday, May 7, 2011, 2:24 PM
> Hi its me again
> 
> I don't mean to get on your nerves, but the use of R proofs
> to be a bit more
> complicated than envisaged.
> 
> I would like to calculate the mean of a group of values,
> here
> "wage_accepted". The group is determined by the stage and
> period, so in the
> end there should be a column with the values of the wages
> in period 1
> stage1, period 1 stage 2, period 2 stage1... Unfortunately,
> I haven't much
> of a clue on how to program this. Could you tell me how the
> function should
> roughly look like – if-else, loops included or not – in
> the end ?
> 
>    treatment session period stage
> wage_accepted type
> 1          1   
>    1      1 
>    1           
> 25  low
> 2          1   
>    1      1 
>    1           
> 19  low
> 3          1   
>    1      1 
>    1           
> 15  low
> 4          1   
>    1      1 
>    2           
> 32 high
> 5          1   
>    1      1 
>    2           
> 13  low
> 6          1   
>    1      1 
>    2           
> 14  low
> 7          1   
>    1      2 
>    1           
> 17  low
> 8          1   
>    1      2 
>    1           
> 12  low
> 
> I am also very grateful if someone could point out a good
> internet tutorial
> resource for R functions such as if-else and loops and how
> to use them in
> conjunction with tables. It should contain simple examples
> if possible. 
> 
> As ever indepted to you,
> 
> Matthias
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/how-to-calculate-the-mean-of-a-group-in-a-table-tp3505986p3505986.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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