st: Collapse an unbalanced panel with annual entries into a standard 5-year average dataset

[Mads Knudsen <madsfloeknudsen@gmail.com>]

Dear stata experts,

Here comes a rookie question which I haven't been able to find an answer
for in the forum so far (please excuse me if I have overlooked the obvious
answer):

What I want to do is the quite standard operation of calculating 5-year and
3-year means by country id. I believe that Jeanty's module "paverage" does
the job if one has a balanced panel dataset. However it does not seem to
work for my unbalanced panel.

To illustrate:
I have a data set of this kind (an unbalanced panel in long format):

Country          Year          GDP          POP
AFG              1950             2               6
AFG              1951                              7
AFG              1952             2               4
AFG              1953             2               3
AFG              1954             6               6
AFG              1955             4               7
ALB               1950            9               9
ALB               1951            8               6
ALB               1952           10
ALB               1953           12               3
ALB               1954           13               2
ALB               1955                             5

which I would like to (easily) transform into a calculated dataset of
the following kind:

country    period          GDP3yrav       POP3yrav
AFG         1950-52         2              5,666667
AFG         1953-55         4              5,333333
ALB          1950-52         9                 7,5
ALB          1953-55       12,5           3,333333

Any help would be highly appreciated. Thank you for your consideration!

Kind regards,
Mads Knudsen
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