I have the following array: 3 dimensional object, one dimension being year.
Object is 3*3*3
library(plyr, reshape)
a1<-rep(c(2007,2008,2009),9)
a2<-c(rep("a",9),rep("b",9),rep("c",9))
a3<-c(rep(c(rep(1,3),rep(2,3),rep(3,3)),3))
a4 <- rnorm(27)
A<-data.frame(cbind(comp=a2,val=a3, year=a1, a4))
A1<-melt(A, id=c("year", "comp", "val"))
A2<-cast(A1, comp~val~year)
I would now like to look for changes from one year to the other, i.e.
"for(i in levels(A$year))
A2[,,i]-A2[,,i-1]"
and put that into A3.
Which should work except for the first one, i.e. giving me a 3*3*2 object
A3.
The more abstract formulation would possibly be cellwise operation within
adjacent matrices of the array. I have however searched the forum for the
key words and there is not much.
Any help even in form of a reference would be appreciated.
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