I've done stuff like this before but it's been a while and I'm stuck. Suppose I have a matrix with one column x and another column y and both are numeric and let the row index of the matrix be i Starting at index i ( i would equal on the first iteration ) when the cumulative sum of x_i+1 - x_i is greater than W = some constant, I want to mark that spot in the row, call it i^* and sum all the values in y between i and i^* and put that value a third column z. Otherwise, the values in the indices of z between i and i^*-1 should be NA. Then, start at i^*+1 and do the same thing again. and keep doing thisn until I get all the way through the rows of the matrix. I think this is tricky but I used to do it and I forgot how to. If it has to be done using loops, that's okay but from previous experience, I don't think looping is necessary. Thanks. Mark
********************************************************************** This email and any files transmitted with it are confidentia...{{dropped}} ______________________________________________ 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