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

[Dimitri Liakhovitski]

Thanks a lot for your helpful suggestion!
Dimitri

On Wed, Jan 20, 2010 at 5:56 PM, Chuck Cleland <ccleland at optonline.net> wrote:
> 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.
> NDRI, Inc. (www.ndri.org)
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-- 
Dimitri Liakhovitski
Ninah.com
Dimitri.Liakhovitski at ninah.com