Is there an R function for the element-wise summation of the matrices stored as elements in single list object? [duplicate]

Answer 1

See ?Reduce.

From the example:

## A general-purpose adder:
add <- function(x) Reduce("+", x)

Then you can

add(myList)

Answer 2

For those interested:

ffoo<-function(jloop){
barlist<-matrix(nr=25,nc=40)
for (jj in 1:jloop) barlist<-barlist+foolist[[jj]]
}

baradd <- function(x) Reduce("+", x)

Leads to:

Rgames> foo<-matrix(1:1000,25)
Rgames> for (jj in 1:5e5) foolist[[jj]]<-foo
Rgames> system.time(baradd(foolist))
   user  system elapsed 
    1.7     0.0     1.7 

Rgames> system.time(ffoo(1e5))
   user  system elapsed 
    0.3     0.0     0.3

Answer 3

> do.call("+", myList)
     [,1] [,2] [,3]
[1,]   11   44   77
[2,]   22   55   88
[3,]   33   66   99

But it fails for more than two which I why I upvoted GSee's answer.

Answer 4

Alternatively, you could put the data in a multi-dimensional array instead of a list, and use apply on that.

require(abind)
m = abind(matrix(1:9,3,3), matrix((1:9)*10,3,3), along = 3)

yields a three dimensional array. Then use apply:

apply(m, 1:2, sum)

Disclaimer: I did not test this code as I do not have R available right now. However, I do wanted you to be aware of this option.