On 6/14/05, Kerry Bush <[EMAIL PROTECTED]> wrote: > Dear helpers in this forum, > > I have the following question: > > Suppose I have the following data set: > > id x y > 023 1 2 > 023 2 5 > 023 4 6 > 023 5 7 > 412 2 5 > 412 3 4 > 412 4 6 > 412 7 9 > 220 5 7 > 220 4 8 > 220 9 8 > ...... > > and i want to calculate sum_{i=1}^k > sum_{j=1}^{n_i}x_{ij}*y_{ij} > > is there a simple way to do this within and between > subject summation in R?
You didn't make it clear what the indices i and j refer to. It seems that part of the answer could use > samp id x y 1 23 1 2 2 23 2 5 3 23 4 6 4 23 5 7 5 412 2 5 6 412 3 4 7 412 4 6 8 412 7 9 9 220 5 7 10 220 4 8 11 220 9 8 > with(samp, tapply(x*y, id, sum)) 23 220 412 71 139 109 but if you then sum this result you simply get the sum of x * y. ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html