one solution is to set NAs to 0, e.g.,

m <- matrix(1:3, 3, 3)
x <- list(m, m+3, m+6)
x[[1]][1] <- NA

x. <- lapply(x, function (x) {x[is.na(x)] <- 0; x} )
Reduce("+", x.)


I hope it helps.

Best,
Dimitris


On 5/4/2012 11:19 AM, Evgenia wrote:
I have a list ( in my real problem  a double list y[[1:24]][[1:15]] but I
think the solution would be the same)

m<- matrix(1:3, 3, 3)
x<- list(m, m+3, m+6)
  and as I want to have the sum of elements I use Reduce(`+`, x)
having as result

Reduce(`+`, x)
      [,1] [,2] [,3]
[1,]   12   12   12
[2,]   15   15   15
[3,]   18   18   18

How can I take the sum of the list elements ignoring NA element
For example if I have
x[[1]][1]<-NA

Then I want to have
      [,1] [,2] [,3]
[1,]  11   12   12
[2,]   15   15   15
[3,]   18   18   18

instead of

Reduce(`+`, x)
      [,1] [,2] [,3]
[1,]   NA   12   12
[2,]   15   15   15
[3,]   18   18   18

Thanks in advance

Evgenia



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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
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