How would I create an `ID3` column for any overlapping `ID1/ID2` column? (Not just the intersection, but for the union set. 

For example, `ID2` is an account number online, and `ID2` is an IP address that a person used to log on. I would like to specify that as long as it was a same IP address OR the log-on ID, the rows are assigned the same `ID3`.

I am using SAS to code. 

HAVE

```
Year    ID2     ID1 
2010    1       201 
2010    1       202 
2010    2       203 
2011    3       202 
2011    4       203 
2011    5       204 

```

WANT 

```
Year    ID3     ID2     ID3
2010    101     1       201
2010    101     1       202
2010    102     2       203
2011    101     3       202
2011    102     4       203
2011    105     5       204

```