Product between all combinations of a vector's elements

Question

Suppose I have a vector c(1, 2, 3, 4) with no duplicated values. I need a vector c(1 * 2, 1 * 3, 1 * 4, 2 * 3, 2 * 4, 3 * 4), so the multiplication

Answer 1

We can use combn with anonymous function call

combn(vec, 2, FUN = function(x) x[1] * x[2])
#[1]  2  3  4  6  8 12

data

vec <- 1:4