Hi Adrienne, I guess apply should be better than for loop.
Code like this: event.gen2 = function(genmat,use1,use2,num,ortho_obs_used){ onerow.gen <- function(one.row, use1....){ one.row[num] <- ifelse(...} genmat[,num] <- NA ##Add one row with NA values apply(genmat[-1,],1,onerow.gen,use1=...)} And R looks TRUE as 1 and FALSE as 0, we may take advantage of it. Regards, Wu ----- A R learner. -- View this message in context: http://r.789695.n4.nabble.com/Running-something-without-a-loop-when-the-result-from-the-previous-iteration-is-require-for-the-currn-tp2321526p2321688.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.