I have two data frames like so:
A B
1 6
2 7
5 4
3 3
9 9
and the other one:
A C
1 5
5 9
3 1
9 1
and I want to merge them to create
A B C
1 6 5
5 4 9
3 3 1
9 9 1
notice that in the merged version, there is no A=2 because this does not show up in the second data frame (even though it shows up in the first). So basically, I want it to merge what exists, and leave out what doesn't. Currently, the merge fails completely because the two A columns are not exactly the same.