This isn’t really a teaching question, but for your particular case IIYC, just multiply the squared quantity by data[,2] before summing. For more general cases, take a look at ifelse().
> On Jul 21, 2016, at 11:20 AM, Steven Stoline <[email protected]> wrote: > > Dear All: good morning > > I do need your help how to do the following calculation: > > Assume we have a matrix 13x2 (say). Two columns named dataval and index > > dataval index > 20 1 > 11 0 > 34 0 > 54 1 > 76 1 > 76 0 > 61 1 > 88 1 > 91 0 > 11 0 > 23 1 > 45 1 > 53 0 > > data<-matrix(c(20,11,34,54,76,76,61,88,91,11,23,45,53,1,0,0,1,1,0,1,1,0,0,1,1,0),13,2) > > data > > I need to perform the calculation: > > for a = 7 (say) > > sum((data[ ,1] - a)^2) > > only for index = data[ ,2] = 1 > > > I am expecting the result to be equal to: > > (20-7)^2 + (54-7)^2+(76-7)^2+(61-7)^2+(88-7)^2+(23-7)^2+(45-7)^2 = 18316 > > > Any helps will be highly appreciated. > > > with many thanks > steve > ------------------------- > Steven M. Stoline > 1123 Forest Avenue > Portland, ME 04112 > [email protected] > > [[alternative HTML version deleted]] > > _______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-sig-teaching _______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-sig-teaching
