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.
 
     
    