Here are data frames that I have:

```
Symbols    Val
  AA        5
  AA        6
  BB        7
  BB        9 
  CC        8
  CC        7

Symbols    Val
  AA        2
  AA        34
  CC        41
  CC        1

```

I'm going to combine two data frames, but first one has some more data in Symbols column. As you see "BB"s are unique compared to second data frame. So, I need to remove two rows (BB) in the first one.
I know how to remove in one data frame, not in two different one. Anybody know how to do it?