[R] standardizing one variable by dividing each value by the mean - but within levels of a factor

[Chuck Cleland]

On 1/20/2010 5:37 PM, Dimitri Liakhovitski wrote:
> Hello!
> 
> I have a data frame with a factor and a numeric variable:
> 
> x<-data.frame(factor=c("b","b","d","d","e","e"),values=c(1,2,10,20,100,200))
> 
> For each level of "factor" - I would like to divide each value of
> "values" by the mean of "values" that corresponds to the level of
> "factor"
> In other words, I would like to get a new variable that is equal to:
> 1/1.5
> 2/1.5
> 10/15
> 20/15
> 100/150
> 200/150
> 
> I realize I could do it through tapply starting with:
> factor.level.means<-tapply(x$values,x$factor,mean) ... etc.
> 
> 
> But it seems clunky to me.
> Is there a more elegant way of doing it?

> with(x, ave(x=values, factor, FUN=function(x){x/mean(x)}))
[1] 0.6666667 1.3333333 0.6666667 1.3333333 0.6666667 1.3333333

?ave

> Thanks a lot!

-- 
Chuck Cleland, Ph.D.
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