st: Create the count of occurances in a panel

[wying1@umbc.edu]

Dear users,

I have a list of person ids as follows.

   1.         4001
   2.         4001
   3.         4001
   4.         4002
   5.         4002
   6.         4003
   7.         4003
   8.         4003
   9.         4003
  10.         4004
  11.         4004
  12.         4004
  13.         4008
  14.         4172
  15.         4172

  The number of occurances represents the years they are in a panel
dataset.  For example, person 4001 have appeared three years in the
panel, and person 4003 has occured four years in the panel.

I am trying to create a count of years those individuals occur in the
panel, i.e., 3 for person 4001, 4 for person 4003, 3 for person 4004, 1
for person 4008, etc.  I have some thoughts to do this by reshaping the
data, but doubt that is the most efficient way to do. Is there any fast
way to do it in STATA?


Thanks,
Ying

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