Hi Ahmed, Your problem appears trivial as you have already specified the form of the calculation.
Learn how to "extract" specified elements from a data structure: # first value sum(dataset1$NPP[dataset1$date >= date1 & dataset1$date <= date2]) # second value dataset2$biomass[dataset2$date == date2] - dataset2$biomass[dataset2$date == date1] # third value dataset3$littfall[dataset3$date == date2] Note that you may have to convert character strings to dates to do the above - see a function like "as.Date". Obviously I do not know the actual names of your datasets and I am assuming that the variable names you have given are the actual ones. Jim On Thu, Jun 22, 2017 at 4:19 AM, Ahmed Attia <ahmedati...@gmail.com> wrote: > Hi R users, > > I need your help to write a code in r that does the following > calculation from three different datasets; > > ac = 1/sum (NPP from date 1 to date 2, dataset=1) * (biomass at date 2 > -biomass at date 1, dataset = 2) + (littfall at date 2, dataset=3). > > all the dates are in yr-month-day format. Which library or function > Should I use to tell R do these calculations of these variables at > different dates. > > I appreciate your help. > > Ahmed Attia, Ph.D. > Agronomist & Soil Scientist > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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 -- To UNSUBSCRIBE and more, see 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.