It looks like I should read the documentation a bit more carefully. Simply ignoring the NA values when calculating the mean *is* a much better solution. (Although having 10 values out of a vector of 40000 or so set to zero is *not* going to bias the mean toward zero in any significant way.)
Thanks to everyone for your help. Reuben ______________________________________________ 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.
