array addition

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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