R help - Jun 2017 - For loop

Hello R users,

The code below is for loop in R that I want to do to following
calculation at each time i and i-1 in 2:75 dataset
(Litterfall_Ahmed97).


ac = ((LeafBiog at date i
-LeafBiog at date i-1, dataset = leafbiom97) + (littperiod at date i,
dataset= Litterfall_Ahmed97))/(sum (GPP from date i-1 to date i,
dataset=GPP_Ahmed13)/2) .

#code for loop

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')
for (i in 2:75){
  (leafbiom97$LeafBiog[leafbiom97$Date == "i"] -
     leafbiom97$LeafBiog[leafbiom97$Date == "i-1"]+
     Litterfall_Ahmed97$littperiod[Litterfall_Ahmed97$Date =="i"])/
    (sum(GPP_Ahmed13$GPP[GPP_Ahmed13$Date >= "i-1" &
                           GPP_Ahmed13$Date <= "i"])/2)
}


#Error in charToDate(x) :

Thanks for your help


Ahmed Attia, Ph.D.
Agronomist & Soil Scientist

Hello,

Without correcting your code, it's obvious that the expressions like 
leafbiom97$Date == "i" and all others with"i" and "i -
1" are wrong.
leafbiom97$Date is of class Date, not character. And, besides,
for(i in ...) makes of i a numeric variable that has nothing to do with 
"i". This "i" will remain the character string "i"
for all iterations of
the loop.

Hope this helps,

Rui Barradas

Em 22-06-2017 17:50, Ahmed Attia escreveu:
> leafbiom97$Date == "i"

For a reproducible example, you need to give us some example data, at least

dput(head(leafbiom97))
dput(head(Litterfall_Ahmed97))
dput(head(GPP_Ahmed13))


Dan

Daniel Nordlund, PhD
Research and Data Analysis Division
Services & Enterprise Support Administration
Washington State Department of Social and Health Services

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Ahmed
> Attia
> Sent: Thursday, June 22, 2017 9:50 AM
> To: r-help
> Subject: [R] For loop
> 
> Hello R users,
> 
> The code below is for loop in R that I want to do to following
> calculation at each time i and i-1 in 2:75 dataset
> (Litterfall_Ahmed97).
> 
> 
> ac = ((LeafBiog at date i
> -LeafBiog at date i-1, dataset = leafbiom97) + (littperiod at date i,
> dataset= Litterfall_Ahmed97))/(sum (GPP from date i-1 to date i,
> dataset=GPP_Ahmed13)/2) .
> 
> #code for loop
> 
> 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')
> for (i in 2:75){
>   (leafbiom97$LeafBiog[leafbiom97$Date == "i"] -
>      leafbiom97$LeafBiog[leafbiom97$Date == "i-1"]+
>      Litterfall_Ahmed97$littperiod[Litterfall_Ahmed97$Date
=="i"])/
>     (sum(GPP_Ahmed13$GPP[GPP_Ahmed13$Date >= "i-1" &
>                            GPP_Ahmed13$Date <= "i"])/2)
> }
> 
> 
> #Error in charToDate(x) :
> 
> Thanks for your help
> 
> 
> Ahmed Attia, Ph.D.
> Agronomist & Soil Scientist
> 
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