st: create a _n time variable panel data

["Ricardo Guimaraes" <ricardo.guimaraes@uni-bonn.de>]

Dear Members,
I have the following panel data .

                                            ?????????????
                                          how to 
calculate
     | t        idd 	i 	v1     v2  |   vn     ob |
     |---------------------------------------------------|
  1. | 1        560036 	1 	3 	.  |	1 	4|
  2. | 1        560036 	2 	2 	.  |	1 	4|
  3. | 1        560036 	3 	3 	1  |	1 	4|
  4. | 1        560036 	4 	6 	1  |	1 	4|
  5. | 1        560036 	5 	3 	1  |	1 	4|
     |---------------------------------------------------|
  6. | 2        560036 	1 	1 	.  |	2 	4|
  7. | 2        560036 	2 	2 	6  |	2 	4|
  3. | 2        560036 	3 	3 	1  |	2 	4|
  8. | 2        560036 	4 	3 	7  |	2 	4|
  9. | 2        560036 	5 	2 	1  |	2 	4|
     |---------------------------------------------------|
  10.| 3        560036 	1 	. 	.  |	. 	.|
  11.| 3        560036 	2 	. 	.  |	. 	.|
  12.| 3        560036 	3 	. 	.  |	. 	.|
  13.| 3        560036 	4 	. 	.  |	. 	.|
  14.| 3        560036 	5 	. 	.  |	. 	.|
     |---------------------------------------------------|
  15.| 4        560036 	1 	1 	.  |	3 	4|
  16.| 4        560036 	2 	2 	.  |	3 	4|
  17.| 4        560036 	3 	7 	1  |	3 	4|
  18.| 4        560036 	4 	3 	1  |	3 	4|
  19.| 4        560036 	5 	5 	1  |	3 	4|
     |---------------------------------------------------|
  20.| 5        560036 	1 	1 	.  |	4 	4|
  21.| 5        560036 	2 	2 	.  | 	4 	4|
  22.| 5        560036 	3 	8 	1  |	4 	4|
  23.| 5        560036 	4 	3 	1  |	4 	4|
  24.| 5        560036 	5 	3 	1  |	4 	4|
     |---------------------------------------------------|


"t" is time (let's say, by month); "idd" identifies a 
family; "i" an individual in the family;
"V1", "v2" are variables about characteristics of 
individuals. The panel is formulated in
a rotating basis: families are observed no more than 4 
times (months) in a year. In my table
they would be the variable "ob". However, the observation 
are not taken in a row. They "jump"
some months (like month 3 in my example), where the 
members of the family are not observed. I do not have the 
variables "Vn" and "ob".
  
Question:

How to create two variables, 1) "vn": 2) "ob" ) for each 
individual saying:

1) "vn" :  a sequence (_n) of the months that the 
individuals are observed. For instance, in the
time "t" the individuals of the family were not observed.
2) "ob" : the total number (_N) of times that the 
individual were observed. Note that in some
variables the values are (.), but the individual was 
observed.

 
sincerely,

ricardo
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