[R-sig-Geo] Multiply 2 raster without considering cells with NA

[Antonio Rodriges]

Try smth like this (I did not run that and not sure in syntax)
r <- overlay(MeanT, cumulP, fun=function(x,y){if (isNA(x) || isNA(y))
return NA else return(y/(x+10))})
Kind regards,
Antonio Rodriges


2015-05-10 1:35 GMT+03:00 sadaoui <sadaouimahrez at outlook.com>:
> Hello,
>
> I try to multiply 2 raster (temperature and precipitation) with "overay"
> function, but the problem at the same time it multiplies the NA values, then
> it gives a false result.
>
> I tried with this code ;
>
> library(raster) ;
> T = getData('worldclim', var='tmean', res=0.5, lon=5, lat=45)/10
> MeanT=mean(T)
> MeanT
> # values      : -11.60833, 23.35833  (min, max)
>
> P= getData('worldclim', var='prec', res=0.5, lon=5, lat=45)
> cumulP=sum(P) #values      : 10, 2883  (min, max)
>
> r <- overlay(MeanT, cumulP, fun=function(x,y){return(y/(x+10))})
> r # values      : -108000, 318000  (min, max)
>
> Normally I find the results : ~[0-120]
>
> I searched this page :
> http://www.inside-r.org/packages/cran/raster/docs/overlay
> but is not mentioned.
>
> it is mentioned in the  the "calc" function  but it is applicable only for a
> single raster : http://www.inside-r.org/packages/cran/raster/docs/calc
>
> Thank you in advance for helping me make a calculation between two raster
> without counting NA values.
>
> Best regards
>
>
>
> --
> View this message in context: http://r-sig-geo.2731867.n2.nabble.com/Multiply-2-raster-without-considering-cells-with-NA-tp7588224.html
> Sent from the R-sig-geo mailing list archive at Nabble.com.
>
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