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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

...lation. 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, Ju...