st: creating variable summarizing for each individual properties of other members of a group at t-1

[Erik Aadland <erikaadland@hotmail.com>]

Dear statalist.
 
I need to create a variable that sums for each individual in my dataset the total number of ind_entry of all other individuals at time: yearmonth - 1.
I have attached a small ex of my data structure below. So for instance, given the small dataset below, for ind_id 2 in yearmonth 11 this variable score = 1. But for ind_id 4 in the same yearmonth, the score = 0.
 
I would also like to generate a variable that identifies for each individual the unique number of other individuals in the dataset that have experienced ind_entry = 1 at least once up until time: yearmonth - 1.
 
I am familiar with the following FAQ: http://www.stata.com/support/faqs/data/members.html
 
My data structure is snapshot data in principle like the example below, but some individuals enter the observation window later than others (i.e. in later yearmonths):
 
year    month    yearmonth    ind_id    ind_entry
2003   10         10               2          0
2003   11         11               2          0
2003   12         12               2          0
2004   1          13               2          0
2004   2          14               2          1
2004   3          15               2          0
2003   10         10               4          1
2003   11         11               4          0
2003   12         12               4          1
2004   1          13               4          0
2004   2          14               4          0
2004   3          15               4          0
 
Any and all input is very welcome.
 
Kind regards and all the best.
 
Erik Aadland. 		 	   		  
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