[R] array addition

[Richard.Cotton at hsl.gov.uk]

Try this:

"%add%" <- function(x1, x2)
  {
    dim1 <- dim(x1)
    dim2 <- dim(x2)

    seq1 <- list();for(i in 1:length(dim1)) seq1[[i]]=seq(dim1[i])
    filter1 <- paste(seq1, collapse=",") 
    cmd1 <- paste("out[", filter1, "]", sep="")
    seq2 <- list();for(i in 1:length(dim2)) seq2[[i]]=seq(dim2[i])
    filter2 <- paste(seq2, collapse=",")
    cmd2 <- paste("out[", filter2, "]", sep="")

    out <- array(0, dim=pmax(dim1,dim2)) 
    eval(parse(text=paste(cmd1, "<-", cmd1, "+ x1")))
    eval(parse(text=paste(cmd2, "<-", cmd2, "+ x2")))
    out
  }

x1 <- array(round(5*runif(30)), dim=c(2,3,5))
x2 <- array(round(5*runif(24)), dim=c(3,4,2))
x <- x1 %add% x2

You probably want to add a check to make the dimensions the same, and the 
code needs tidying, but you get the idea.

Regards,
Richie.

Mathematical Sciences Unit
HSL


r-help-bounces at r-project.org wrote on 19/12/2007 09:26:44:

> Hi
> 
> suppose I have two arrays x1,x2 of dimensions a1,b1,c1 and
> a2,b2,c2 respectively.
> 
> I want  x = x1   "+"   x2 with dimensions c(max(a1,a2), max(b1,b2),max 
> (c1,c2))
> 
> with
> 
> x[a,b,c] = x1[a1,b1,c1] + x2[a2,b2,c2] if    a <=min(a1,a2) , b<=min 
> (b1,b2), c<=min(c1,c2)
> 
> and the other bits either x1 or x2 or zero according to whether the 
> coordinates
> are "in range" for x1 or x2 or neither.
> 
> The answer has to work for arbitrary-dimensioned arrays.
> 
> toy example follows (matrices):
> 
> 
>  > x1
>       [,1] [,2] [,3] [,4] [,5]
> [1,]    1    3    5    7    9
> [2,]    2    4    6    8   10
>  > x2
>       [,1] [,2] [,3]
> [1,]    1    4    7
> [2,]    2    5    8
> [3,]    3    6    9
>  > x
>       [,1] [,2] [,3] [,4] [,5]
> [1,]    2    7   12    7    9
> [2,]    4    9   14    8   10
> [3,]    3    6    9    0    0
>  >
> 
> 
> Note the zeros at lower-right.
> 
> 
> Is there a ready-made solution to this?
> 
> 
> 
> 
> 
> --
> Robin Hankin
> Uncertainty Analyst and Neutral Theorist,
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
>   tel  023-8059-7743
> 
> ______________________________________________
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> PLEASE do read the posting guide 
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