outer() equivalent for non-vector lists in R

Question

I understand how outer() works in R:

> outer(c(1,2,4),c(8,16,32), \"*\")

     [,1] [,2] [,3]
[1,]    8   16   32
[2,]   16   32   64
[3,]   32   64  128
         


        

Answer 1

Just use the for loop. Any built-in functions will degenerate to that anyway, and you'll lose clarity of expression, unless you carefully build a function that generalises outer to work with lists.

The biggest improvement you could make would be to preallocate the matrix:

M <- list()
length(M) <- numElements ^ 2
dim(M) <- c(numElements, numElements)

PS. A list is a vector.