合并 data.frame 但只保留唯一的列？

假设我想合并两个 data.frames，但有些列是多余的（相同）。我如何合并这些 data.frames 但删除冗余列？

X1 = data.frame(id = c("a","b","c"), same = c(1,2,3), different1 = c(4,5,6))
X2 = data.frame(id = c("b","c","a"), same = c(2,3,1), different2 = c(7,8,9))


merge(X1,X2, by="id", all = TRUE, sort = FALSE)




id same.x different1 same.y different2
1  a      1          4      1          9
2  b      2          5      2          7
3  c      3          6      3          8

但是我怎样才能得到 different1 和 different2 列呢？

id same different1 different2
1  a    1     4      9
2  b    2     5      7
3  c    3     6      8

您可以在 by 参数中包含相同的列。默认为by=intersect(names(x), names(y)). Try merge(X1, X2)（它与merge(X1, X2, by=c("id", "same"))):

 merge(X1,  X2)
 #  id same different1 different2
 #1  a    1          4          9
 #2  b    2          5          7
 #3  c    3          6          8