[R] how to assign a group mean to individual cases?

[Greg Snow]

For the first question use ave along with mean like Gabor suggested.

For the second question (finding the mean with that value removed) you
can use ave with the sum function ("ave(x, group, FUN=sum)") to find the
sum rather than the average, then use ave again with the length function
to find out how many are in each group, then subtract your x value from
the sum to get the sum of all other values in the group and divide that
sum by n-1 (from using ave with length) to get the mean.

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 
 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Casey Klofstad
> Sent: Monday, November 12, 2007 3:02 PM
> To: r-help at r-project.org
> Subject: [R] how to assign a group mean to individual cases?
> 
> I need advice on how to create a variable that is the group 
> mean of another variable.
> 
> For example, I have a variable called x for which each row in 
> the data set has a value. I also have a nominal variable 
> called g that indicates which of 100 different groups each 
> row belongs to.
> 
> So, I want to create a new variable called w, which is the 
> group mean of x for which ever group the row belongs to (as 
> indicated by variable g). Ideally, I'd also like to take out 
> each row's value of x before calculating the group mean 
> assigned to that row.
> 
> I've already tried the aggregate command. That gives me the 
> group means, but does not allow me to assign them to each row 
> in the data set.
> 
> THANKS!
> --
> Casey A. Klofstad
> University of Miami
> Department of Political Science
> Coral Gables, FL
> 
> klofstad at gmail.com
> http://moya.bus.miami.edu/~cklofstad
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>