[R] Computing Water Balance using a loop.

[Frederic Ntirenganya]

Dear Duncan,

Those condition should be there and also look at Rainfall and evaporation
columns.
If i change it to be like the following loop, it can't do it.

The problem is how to include those conditions and also respect the formula?

wb=c()
for (w in 1:length(Wb30$Water_Balance)){
  if(w<0){
   w=0
  }

 wb=Wb30$Water_Balance[w-1] + Wb30$Rainfall[w]-Wb30$Evaporation[w]
}
wb

Regards,
Frederic.

Frederic Ntirenganya
Maseno University,
African Maths Initiative,
Kenya.
Mobile:(+254)718492836
Email: fredo at aims.ac.za
https://sites.google.com/a/aims.ac.za/fredo/

On Thu, Oct 23, 2014 at 3:44 PM, Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:

> On 23/10/2014, 8:33 AM, Frederic Ntirenganya wrote:
> > Dear All,
> >
> > I want to calculate water balance using the following formula:
> > Water balance today = Water balance yesterday + Rainfall − Evaporation
> >
> > This is a sample of data I am using:
> >
> > head(Wb30)
> >   May Rainfall Evaporation Water_Balance
> > 1   7        0           5             0
> > 2   8       10           5            NA
> > 3   9        0           5            NA
> > 4  10        0           5            NA
> > 5  11        2           5            NA
> > 6  12       23           5            NA
> >
> > The following is the loop am trying to use but it is not working well.
> >
> > #Water balance today = Water balance yesterday + Rainfall − Evaporation
> > #If Water balance today < 0 then Water balance today = 0
> > #If Water balance today > 100 then Water balance today = 100
> > wb=c()
> > for (w in 1:length(Wb30$Water_Balance)){
> >   if(w<0 & w>100){w<-0 & w<-100}
>
> The line above doesn't make sense.  It is impossible for w to be both
> less than 0 and greater than 100, so the condition will never be true.
> And if it is true, "w<-0 & w<-100" is not a sensible thing to do.
>
> >   #print (w);
> >  for (i in 1:length(Wb30$Rainfall)){
> >     for (j in 1:length(Wb30$Evaporation)){
> >     }
> >   }
>
> Those loops do nothing.
>
> >  wb<-Wb30$Water_Balance[w] + Wb30$Rainfall[i+1]-Wb30$Evaporation[j+1]
>
> Those should be using w-1 in place of w, and w in place of i+1 and j+1.
>
> Duncan Murdoch
>
> > }
> > wb
> >
> > Any suggest of what I am missing for it to work correctly is welcome.
> >
> >
> > Regards,
> >
> > Frederic Ntirenganya
> > Maseno University,
> > African Maths Initiative,
> > Kenya.
> > Mobile:(+254)718492836
> > Email: fredo at aims.ac.za
> > https://sites.google.com/a/aims.ac.za/fredo/
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > 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.
> >
>
>

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