Pete The original question "I would like to calculate the average of the mean temperature for the summer months (Juli, August, September) for each of the 20 years"
Your codes gives mean for each of the 3 months, not for the 20 summers. Here is a way to get the summer average for each of the 20 years: set.seed = 1 d=data.frame(year=rep(1980:1999,each=12), month=rep(1:12,20), meanTemp = rnorm(240,10,5)) sum_d <- subset(d, d[,2]>=7 & temp_df[,2] <=9) aggregate(meanTemp ~ year, data = sum_d, mean) -- View this message in context: http://r.789695.n4.nabble.com/Calculate-a-mean-for-several-months-for-several-years-tp3318363p3318567.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.
