Hi Jim, Thank you very much, this was so helpful.
GPP_Ahmed13$Date <- as.Date(GPP_Ahmed13$Date, '%Y/%m/%d') Litterfall_Ahmed97$Date <- as.Date(Litterfall_Ahmed97$Date, '%Y/%m/%d') leafbiom97$Date <- as.Date( leafbiom97$Date, '%Y/%m/%d') (leafbiom97$LeafBiog[leafbiom97$Date == "2012-02-12"] - leafbiom97$LeafBiog[leafbiom97$Date == "2010-03-15"]+ Litterfall_Ahmed97$littperiod[Litterfall_Ahmed97$Date =="2011-04-08"])/ (sum(GPP_Ahmed13$GPP[GPP_Ahmed13$Date >= "2010-03-12" & GPP_Ahmed13$Date <= "2012-04-12"])/2) Best regards Ahmed Ahmed Attia, Ph.D. Agronomist & Soil Scientist On Thu, Jun 22, 2017 at 12:24 AM, Jim Lemon <drjimle...@gmail.com> wrote: > Hi Ahmed, > Your problem appears trivial as you have already specified the form of > the calculation. > > Learn how to "extract" specified elements from a data structure: > > # first value > sum(dataset1$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.
