R help - Jun 2007 - getting tapply() to work across multiple columns

I have the following data.frame:

index <-
c("a","a","b","b","b")
alpha <- c(1,2,3,4,5)
beta <- c(2,3,4,5,6)
table <-data.frame(index,alpha,beta)

I'm now interested in getting means of alpha and beta for each of the
index values and do a tapply() for each of the columns, e.g.

means.alpha <- tapply(table$alpha, index,mean)
means.beta <- tapply(table$beta,index,mean)

but as one tapply function, something like

tapply(table[2:3], index, mean), but this clearly doesnt' work.

Suggestions?

Thanks,
Andrew

Try aggregate:

aggregate(table[2:3], table[1], mean)


On 6/17/07, Andrew Yee <yee at post.harvard.edu>
wrote:
> I have the following data.frame:
>
> index <-
c("a","a","b","b","b")
> alpha <- c(1,2,3,4,5)
> beta <- c(2,3,4,5,6)
> table <-data.frame(index,alpha,beta)
>
> I'm now interested in getting means of alpha and beta for each of the
> index values and do a tapply() for each of the columns, e.g.
>
> means.alpha <- tapply(table$alpha, index,mean)
> means.beta <- tapply(table$beta,index,mean)
>
> but as one tapply function, something like
>
> tapply(table[2:3], index, mean), but this clearly doesnt' work.
>
> Suggestions?
>
> Thanks,
> Andrew
>
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