try this. The first group of lines recreates your data frame, DF, and the last line is the aggregate:
Input <- "Date Time z 2006-01-01 21:00 6,2 2006-01-01 22:00 5,7 2006-01-01 23:00 3,2 2006-01-02 00:00 7,8 2006-01-02 01:00 6,8 2006-01-02 02:00 5,6 2007-03-30 22:00 5,2 2007-03-30 23:00 8,3 2007-03-31 00:00 6,4 2007-03-31 01:00 7,4 " DF <- read.table(textConnection(Input), header = TRUE, as.is = TRUE) DF$z <- as.numeric(sub(",", ".", DF$z)) DF$Date <- as.Date(DF$Date) aggregate(DF["z"], list(yearmon = format(DF$Date, "%Y-%m")), mean) On 4/23/07, Michel Schnitz <[EMAIL PROTECTED]> wrote: > Hello, > > is there a way to use the aggregate function to calculate monthly mean > in case i have one row in data frame that holds the date like > yyyy-mm-dd? i know that it works for daily means. i also like to do it > for monthly and yearly means. maybe there is something like aggregate(x, > list(Date[%m]), mean)? > the data frame looks like: > > Date Time z > 2006-01-01 21:00 6,2 > 2006-01-01 22:00 5,7 > 2006-01-01 23:00 3,2 > 2006-01-02 00:00 7,8 > 2006-01-02 01:00 6,8 > 2006-01-02 02:00 5,6 > . > . > . > 2007-03-30 22:00 5,2 > 2007-03-30 23:00 8,3 > 2007-03-31 00:00 6,4 > 2007-03-31 01:00 7,4 > > thanks for help! > -- > Michél Schnitz > [EMAIL PROTECTED] > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > ______________________________________________ R-help@stat.math.ethz.ch 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.