is your data a data frame or a matrix? do you want to compute the differences columnwise, i.e., for each column independently? consider this example:
# generate and display dummy data (d = as.data.frame(replicate(3, sample(5)))) # compute successive differences columnwise as.data.frame(apply(d, 2, diff)) apply(as.matrix(d), 2, diff) see ?apply and ?diff for details. note that apply will return a matrix both when given a data frame and when given a matrix. vQ Rafael Moral wrote: > Dear useRs, > I'm trying to write a loop to sum my data in the following way: > (the second - the first) + (the third - the second) + (the fourth - the > third) + ... > for each column. > > So, I wrote something like this: > > c <- list() > for(i in 1:ncol(mydata)) { > for(j in 2:nrow(mydata)) { > c[[i]] <- sum(yc[j,i] - yc[(j-1),i]) > }}} > > As for the columns it works pretty fine, but it only returns the last > subtraction, however, I need the sum of all subtractions. > > Any ideas? > > Regards, > Rafael. > > > Veja quais são os assuntos do momento no Yahoo! +Buscados > > [[alternative HTML version deleted]] > > > ------------------------------------------------------------------------ > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help ______________________________________________ R-help@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.