This comes as an application to this question: http://stackoverflow.com/questions/5896648/sum-object-in-a-column-between-an-interval-defined-by-another-column/5897695#comment23166107_5897695
What I would like to know is how to adjust the answer if I want to sum the values in B, for ((A[i+1]-A[i]==0) or (A[i+1]-A[i]==1) or (A[i]-A[i-1]==0) or (A[i]-A[i-1]==1)) where i is the row index, so basically sum B rows for A-s that have the same value +/- 1, but not sum the same row twice? I tried building a loop function but I get stuck when using row indices with data frames. So if I have the next data frame: df A B [1,] 1 4 [2,] 1 3 [3,] 3 5 [4,] 3 7 [5,] 4 3 [6,] 5 2 The result I would obtain(considering that when I have ), would be: df A B [1,] 1 7 [2,] 3 15 [3,] 5 2 - Nanami [[alternative HTML version deleted]] ______________________________________________ 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.