How to cross-paste all combinations of two vectors (each-to-each)?

Question

I need to paste all combinations of elements from two character vectors, \"each\" to \"each\": instead of

> paste0(c(\"a\", \"b\"), c(\"c\", \"d\"))
[1]          


        

Answer 1

Another (less generally useful) incantation:

levels(interaction(x,y,sep=""))
# [1] "ac" "bc" "ad" "bd"