merge関数を使う
> x <- data.frame(id = c(1,2,3), name = c("a", "b", "c"))
> y <- data.frame(id = c(1,2,3,4), age = c(12, 10, 11, 9))
> merge(x, y, "id")
id name age
1 1 a 12
2 2 b 10
3 3 c 11
> merge(x, y, "id", all = T)
id name age
1 1 a 12
2 2 b 10
3 3 c 11
4 4 <NA> 9
> 参考
