Array element is function of its position in the array

Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Asher Meir
> Sent: Thursday, December 29, 2011 1:58 PM
> To: r-help at r-project.org
> Subject: [R] Array element is function of its position in the array
> 
> I want to create a new array which selects values from an original
> array
> based on a function of the indices. That is:
> 
> I want to create a new matrix Vnew[i,j,k]=Vold[i,j,ks] where ks is a
> function of the index elements i,j,k. I want to do this WITHOUT a loop.
> 
> Call the function "ksfunction", and the array dimensions nis,njs,nks. I
> can
> do this using a loop as follows:
> 
> # Loop version:
> Vnew<-array(NA,c(nis,njs,nks)
> for(i1 in 1:nis)for(j1 in 1:njs)for(k1 in
> 1:nks)Vnew[i1,j1,k1]<-Vold[i1,k1,ksfunction(i1,j1,k1)]
> 
> I already know how to create an array of the ks's:
> ksarray[i,j,k]=ksfunction(i,j,k)  # I have the array ksarray ready
> 
> I don't want a loop because nis,njs, and nks are pretty large and it
> takes
> forever.
> 
> Would appreciate help with this issue.
> 
> 	[[alternative HTML version deleted]]
> 
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