st: Just another data reshaping problem

[Sascha Robert <sascha.robert@iew.unizh.ch>]

Hi,

Complex data reshaping unfortunately seems to lie beyond my logical 
capabilities... so anyone up to a little brain-teaser?

My data (simplified) looks like this:

time    group_1 ID_g1      group_2    ID_g2
1       0       1          1          2
1       0       1          1          3
1       0       2          1          1
1       1       1          0          1
2...
and so on.

The data says something like (for the first row:) At time 1, ID 1 of 
group 0 encountered ID 2 of group 2. Note that an encounter always 
involves two entities of two different groups.

I would like to reshape the data to the form:

group    ID    num_encounters(*)
0        1     x
0        2     y
1        1     z
...

(*)sum of ALL dyadic encounters where ID participated

Any hint is warmly welcomed.
Sascha

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