Many thanks for the recent answers to my question about pattern recognition. The hint to "grep" and the "pattern" argument brought me a big deal forward.
# Now, I have a data frame: DATE <- c("1930-01-01", "1930-01-01", "1930-02-01", "1931-01-01", "1931-02-01", "1931-03-01") # almost all months until "1999-12-01". Day is always 01, the same months actually occur several times. FREQ <- rep(1,6) ex<- data.frame(DATE,FREQ) # I can aggregate it like this: ex <- tapply(ex$FREQ, ex$DATE, sum) # or use"grep" to extract a single year: # ex[grep(pattern="^1931", ex$DATE),] # But how can I aggregate the years such that a barplot would show me the FREQ per year and not per month? barplot(as.vector(ex)) # Sorry for the bad example, of course my data.frame is much bigger and the barplot gives me a nice monthly time series of events, but I really only want the occurrences per year, not per month. Grateful for your advice! Friderike ______________________________________________ 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.