R help - May 2006 - average by group...

I have a dataframe with 700,000 rows and 2 vectors
(columns): ?group? and ?score?.

I  wish to calculate a third vector of length 700000:
the average score by group.  Even though the avarge
value will repeat, I wish to return the average for
that particular group for each row.

(I know I can do this by calculating each group?s
average and then using the merge command, but as my
calculations get more complex and my data set gets
larger, the merge command seems to be fairly slow.)

?tapply
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of r user
> Sent: Tuesday, May 30, 2006 12:27 PM
> To: rhelp
> Subject: [R] average by group...
> 
> I have a dataframe with 700,000 rows and 2 vectors
> (columns): "group" and "score".
> 
> I  wish to calculate a third vector of length 700000:
> the average score by group.  Even though the avarge value 
> will repeat, I wish to return the average for that particular 
> group for each row.
> 
> (I know I can do this by calculating each group's average and 
> then using the merge command, but as my calculations get more 
> complex and my data set gets larger, the merge command seems 
> to be fairly slow.)
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>

I didn't know about ave(). What about this, though:

dat <- data.frame(score = rnorm(100), group = gl(10,10))
group.score <- with(dat, tapply(score, group, mean))
dat$group.score <- group.score[as.character(dat$group)] 

Harold
> -----Original Message-----
> From: pd at pubhealth.ku.dk [mailto:pd at pubhealth.ku.dk] On 
> Behalf Of Peter Dalgaard
> Sent: Tuesday, May 30, 2006 1:09 PM
> To: Doran, Harold
> Cc: r user; rhelp
> Subject: Re: [R] average by group...
> 
> "Doran, Harold" <HDoran at air.org> writes:
> 
> > ?tapply
> 
> Nope. 
> 
> ?ave
>   
> > 
> > > -----Original Message-----
> > > From: r-help-bounces at stat.math.ethz.ch 
> > > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of r user
> > > Sent: Tuesday, May 30, 2006 12:27 PM
> > > To: rhelp
> > > Subject: [R] average by group...
> > > 
> > > I have a dataframe with 700,000 rows and 2 vectors
> > > (columns): "group" and "score".
> > > 
> > > I  wish to calculate a third vector of length 700000:
>                                         ^^^^^^^^^^^^^^^^
> 
> > > the average score by group.  Even though the avarge value will 
> > > repeat, I wish to return the average for that particular 
> group for 
> > > each row.
> > > 
> > > (I know I can do this by calculating each group's average 
> and then 
> > > using the merge command, but as my calculations get more 
> complex and 
> > > my data set gets larger, the merge command seems to be 
> fairly slow.)
> > > 
> > > ______________________________________________
> > > R-help at stat.math.ethz.ch mailing list 
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide! 
> > > http://www.R-project.org/posting-guide.html
> > >
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> > 
> 
> -- 
>    O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
>   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
>  (*) \(*) -- University of Copenhagen   Denmark          Ph:  
> (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: 
> (+45) 35327907
>