st: Sum of different values per column

[Ziad El-Khatib <ziad.khatib@gmail.com>]

Hi!
It is a cohort dataset, I want to sum one measurement over time, example below:

id            visit            pillcount           sumpc
101           1                 20                    .
101           2                 40                    .
101           3                 20                    80
102
etc..


Any tips how to create sumpc variable?


Thank you and best regards
ziad

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