st: generating variables based on the co-occurrence of ids in groups over time

[Erik Aadland <erikaadland@hotmail.com>]

Dear Statalist.
 
I am struggling to generate two variables based on the co-occurrence of ind_ids in project_ids over time (yearmonth).
 
Structure of my data is as follows:
 
yearmonth    project_id    ind_id
5            1             1
5            1             2
5            1             3
5            2             1
5            2             4
5            2             5
6            3             1
6            3             2
6            3             5
6            4             4
6            4             5
6            4             6
7            5             1
7            5             4
7            5             5
7            5             2

 
The two variables I need to generate are:
 
X (no. of prior collaborators in project for each ind_id): how many of the other individuals in project_id each ind_id has previously collaborated with (i.e. how many of the other ind_ids in the current project that each focal ind_id has co-occurred with in other projects in previous yearmonths) 
 
Z (total prior collaborations in project for each ind_id): the total number of times each ind_id has previously collaborated with the given other individuals in project_id (i.e. the total number of times each focal ind_id has co-occurred with other ind_ids in the current project in previous yearmonths)
 
I have added varible X and Z scores to the data structure example below:
 
yearmonth    project_id    ind_id    X    Z 
5            1             1  
5            1             2  
5            1             3  
5            2             1  
5            2             4  
5            2             5  
6            3             1         2    2
6            3             2         1    1
6            3             5         1    1
6            4             4         1    1
6            4             5         1    1
6            4             6         0    0
7            5             1         3    5
7            5             4         2    3
7            5             5         3    5
7            5             2         2    3


Any and all input to these problems would be greatly appreciated.
 
I use Stata 10 and the panel data is unbalanced.
 
Sincerely,
Erik. 		 	   		  
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