R help - Nov 2009 - By processing on two variables at once?

Hello!

I'm trying to runs stats on two vars at a time in a big data frame.  I knew
how to do this in SAS many years ago, but have half-forgotten that as well!

I need, for instance, mean(value) by x-y combination:
x   y   z   value
1   1   1    10
1   1   2    20
1   2   1    30

with results:
x   y   mean(value)
1   1    15
1   2    30

Any help?

Thanks,

~Zack
-- 
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Hi,

On Wed, Nov 11, 2009 at 8:51 PM, zwarren <zack.warren at yahoo.com>
wrote:
>
> Hello!
>
> I'm trying to runs stats on two vars at a time in a big data frame. ?I
knew
> how to do this in SAS many years ago, but have half-forgotten that as well!
>
> I need, for instance, mean(value) by x-y combination:
> x ? y ? z ? value
> 1 ? 1 ? 1 ? ?10
> 1 ? 1 ? 2 ? ?20
> 1 ? 2 ? 1 ? ?30
>
> with results:
> x ? y ? mean(value)
> 1 ? 1 ? ?15
> 1 ? 2 ? ?30
What happend to your "z" column?

Anyway, there are a few ways you can do this.

1. If you just want to use the standard library, try the aggregate
function. Roghly:

R> df <- data.frame(x=c(1,1,1), y=c(1,1,2), z=c(1,2,1), value=c(10,20,30))
R> aggregate(df, by=list(df$x, df$y), mean)
  Group.1 Group.2 x y   z value
1       1       1 1 1 1.5    15
2       1       2 1 2 1.0    30

2. You can try using the plyr library:

R> library(plyr)
R> ddply(df, .(x, y), mean)
  x y   z value
1 1 1 1.5    15
2 1 2 1.0    30

HTH,
-steve

-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact

On Nov 11, 2009, at 8:51 PM, zwarren wrote:
>
> Hello!
>
> I'm trying to runs stats on two vars at a time in a big data frame.   
> I knew
> how to do this in SAS many years ago, but have half-forgotten that  
> as well!
>
> I need, for instance, mean(value) by x-y combination:
> x   y   z   value
> 1   1   1    10
> 1   1   2    20
> 1   2   1    30
>
> with results:
> x   y   mean(value)
> 1   1    15
> 1   2    30
It's generally a bad idea to incorporate "(" in variable names,
but
it's possible:

 > aggregate(dat$value, list(dat$x, dat$y), mean)
   Group.1 Group.2  x
1       1       1 15
2       1       2 30
 > newdat <-aggregate(dat$value, list(dat$x, dat$y), mean)
 > names(newdat) <-
c("x","y",bquote("mean(value)") )
 > newdat
   x y mean(value)
1 1 1          15
2 1 2          30
>
> Any help?
>
> Thanks,
>
> ~Zack
> -- 
> View this message in context:
http://old.nabble.com/By-processing-on-two-variables-at-once--tp26312115p26312115.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT