我有两个向量：
group1 <- c("a", "b")
group2 <- c("c", "d", "e")
我想要获取“group1”中的一个元素与“group2”中的一个或两个元素的所有组合。
期望的结果是：
"a" "c" # one element from group1, one element from group 2
"b" "c"
"a" "d"
"b" "d"
"a" "e"
"b" "e"
"a" "c" "d" # one element from group1, two elements from group 2
"b" "c" "d"
"a" "c" "e"
"b" "c" "e"
"a" "d" "e"
"b" "d" "e"