Hello, Sorry to all for the lack of communication, and thanks to those with the suggestions.
So I have two matrixes which are different sizes, same column number but different row number. What I would like to do is to compare A to B. In the 6 and 9th column there are ref numbers (molecular masses to be exact). I would like to check A and B by these columns. If I find that the number in A[9,x] and B[9, x] are the same then I want to remove the row that it is comparing from A. So overall, if something appears in B then I remove it from A. Cheers, Paul Research Technician Mass Spectrometry o The / o Scripps \ o Research / o Institute [[alternative HTML version deleted]] ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.