# [R] Help/ Mathematics

Ahmed Attia ahmedatia80 at gmail.com
Thu Jun 22 10:13:26 CEST 2017

```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 <drjimlemon at 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 <ahmedatia80 at 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.
>>
>>
>> Ahmed Attia, Ph.D.
>> Agronomist & Soil Scientist
>>
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