Geoff, I think you could write an if loop to solve this.
You could write: for(i in 1:num_obs){ if(DAYS[i]=='Monday'){ DF$DAYS.BETWEEN[i]<-1 } } Where 'num_obs' is the total number of temperature observations you have. This would only be correct if you had no missing data on Fridays. Also, if you had any missing Mondays, the Tuesday 'DAYS.BETWEEN' would be a 5 instead of a 2. Maybe there's a better way to do this, but I think this should work as long as you have a pretty complete record. Billy -- View this message in context: http://r.789695.n4.nabble.com/days-between-dates-tp3544335p3544643.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.