R help - Apr 2007 - Calculating means in a new table

Dear all -
I imported (on a Mac) a big table with >2000 lines:
> mydata <- read.table(file("/Users/didiw/Desktop/R/all.txt"),
header = TRUE)
> mydata[1:15,]
   location Spezies Spec E.MPa.   Phi No Trial  
1        LC       P    J  13.27  7.51  1     1  
2        LC       P    J  14.24  6.68  1     1  
3        LC       P    J  14.28  7.01  2     1  
4        LC       P    J  16.65  6.30  1     2  
....

Now i want to crate a new table "mymeans" where all means and Stdev 
of E.MPa and Phi when location, Spezies, No, and Trial are the same, 
something like this:

   location Spezies Spec No Trial mean.E	stddev.E	mean.Phi	std.Phi
1        LC       P    J 1     1  xx		xx		xx		xx
2        LC       P    J 2     1  xx		xx		xx		xx  
3        LC       P    J 1     2  xx		xx		xx		xx     
....

Because I we did ca 8 repetition of each measurement, the new table should
have only 2000/8 lines.

Thanks for any help!

-didi

Hi

look at aggregate

something like 

mymean<-aggregate(mydata[,4:5], list( location, Spezies....), mean)
mysd<-aggregate(mydata[,4:5], list( location, Spezies....), sd)

and then cbind(appropriate columns of resulting data frames)

Petr Pikal
petr.pikal at precheza.cz

r-help-bounces at stat.math.ethz.ch napsal dne 24.04.2007 14:04:30:
> Dear all -
> I imported (on a Mac) a big table with >2000 lines:
> > mydata <-
read.table(file("/Users/didiw/Desktop/R/all.txt"), header =
TRUE) 
> > mydata[1:15,]
>    location Spezies Spec E.MPa.   Phi No Trial 
> 1        LC       P    J  13.27  7.51  1     1 
> 2        LC       P    J  14.24  6.68  1     1 
> 3        LC       P    J  14.28  7.01  2     1 
> 4        LC       P    J  16.65  6.30  1     2 
> ....
> 
> Now i want to crate a new table "mymeans" where all means and
Stdev
> of E.MPa and Phi when location, Spezies, No, and Trial are the same, 
> something like this:
> 
>    location Spezies Spec No Trial mean.E   stddev.E   mean.Phi   std.Phi
> 1        LC       P    J 1     1  xx      xx      xx      xx
> 2        LC       P    J 2     1  xx      xx      xx      xx 
> 3        LC       P    J 1     2  xx      xx      xx      xx 
> ....
> 
> Because I we did ca 8 repetition of each measurement, the new table 
should
> have only 2000/8 lines.
> 
> Thanks for any help!
> 
> -didi
> 
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