This should do the trick: data$date <- as.Date(data$date, '%m/%d/%Y') data$month <- format(data$date, '%Y-%m') by(data$rammday, data$month, sum)
Hope that helps, Jason -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Stephan Kolassa Sent: Wednesday, March 31, 2010 2:31 PM To: Steve Murray Cc: r-help@r-project.org Subject: Re: [R] Summing data based on certain conditions ?by may also be helpful. Stephan Steve Murray schrieb: > Dear all, > > I have a dataset of 1073 rows, the first 15 which look as follows: > >> data[1:15,] > date year month day rammday thmmday > 1 3/8/1988 1988 3 8 1.43 0.94 > 2 3/15/1988 1988 3 15 2.86 0.66 > 3 3/22/1988 1988 3 22 5.06 3.43 > 4 3/29/1988 1988 3 29 18.76 10.93 > 5 4/5/1988 1988 4 5 4.49 2.70 > 6 4/12/1988 1988 4 12 8.57 4.59 > 7 4/16/1988 1988 4 16 31.18 22.18 > 8 4/19/1988 1988 4 19 19.67 12.33 > 9 4/26/1988 1988 4 26 3.14 1.79 > 10 5/3/1988 1988 5 3 11.51 6.33 > 11 5/10/1988 1988 5 10 5.64 2.89 > 12 5/17/1988 1988 5 17 37.46 20.89 > 13 5/24/1988 1988 5 24 9.86 9.81 > 14 5/31/1988 1988 5 31 13.00 8.63 > 15 6/7/1988 1988 6 7 0.43 0.00 > > > I am looking for a way by which I can create monthly totals of rammday > (rainfall in mm/day; column 5) by doing the following: > > For each case where the month value and the year are the same (e.g. 3 and > 1988, in the first four rows), find the mean of the the corresponding rammday > values and then times by the number of days in that month (i.e. 31 in this > case). > > Note however that the number of month values in each case isn't always the > same (e.g. in this subset of data, there are 4 values for month 3, 5 for > month 4 and 5 for month 5). Also the months will of course recycle for the > following years, so it's not simply a case of finding a monthly total for > *all* the 3s in the whole dataset, just those associated with each year in > turn. > > How would I go about doing this in R? > > Any help will be gratefully received. > > Many thanks, > > Steve > > > > _________________________________________________________________ > We want to hear all your funny, exciting and crazy Hotmail stories. > Tell us now > > ______________________________________________ > 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. > ______________________________________________ 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. ______________________________________________ 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.
