A slight variation of what Jorge has proposed is:
f <- function(x) c( mu=mean(x), var=var(x) )
do.call( "rbind", tapply( df$value, df$ID, f ) )
mu var
111 4.333333 4.333333
138 6.000000 4.666667
178 5.000000 8.000000
Regards, Adai
Jorge Ivan Velez wrote:
Dear Julia,
Try also
x=read.table(textConnection("ID value
111 5
111 6
111 2
178 7
178 3
138 3
138 8
138 7
138 6"),header=TRUE)
closeAllConnections()
attach(x)
do.call(rbind,tapply(value,ID, function(x){
res=c(mean(x,na.rm=TRUE),var(x,na.rm=TRUE))
names(res)=c('Mean','Variance')
res
}
)
)
HTH,
Jorge
On Thu, Sep 11, 2008 at 1:45 PM, liujb <[EMAIL PROTECTED]> wrote:
Hello,
I have a data set that looks like this.
ID value
111 5
111 6
111 2
178 7
178 3
138 3
138 8
138 7
138 6
.
.
.
I'd like to calculate the mean and var for each object identified by the
ID.
I can in theory just loop through the whole thing..., but is there a easier
way/command which let me calculate the mean/var by ID?
Thanks,
Julia
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and provide commented, minimal, self-contained, reproducible code.
