Find all combinations of one column based on the unique values of another column in a dataframe

Question

Suppose that I have a dataframe

data.frame(v1 = c(1,1,1,2,2,3), v2 = c(6,1,6,3,4,2))
  v1 v2
1  1  6
2  1  1
3  1  6
4  2  3
5  2  4
6  3  2

Is t