Hi,

Suppose I have a dataframe like:
> data
        y    x
1      1 2008
2      1 2008
3      0 2008
4      0 2009
5      1 2009

Now I want to know how much "1" corresponds with 2008 and how much with
2009, the answers are 3 and 1.
How can I achieve this? Thanks for the anwer.
André

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