merge data.frame but keep only unique columns?

Question

Let\'s say I want to merge two data.frames but some of the columns are redundant (the same). How would I merge those data.frames but drop the redundant columns?

Answer 1

You could include the column same in your by argument. The default is by=intersect(names(x), names(y)). Try merge(X1, X2) (it is the same as 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