st: How to construct a duration variable?

["Albert Newton" <lacneo@gmail.com>]

Dear Statalist users,
       I get stuck in coding a during variable.  The data is like:

hhid    weekshoppingday triptype        switch  switchtype      Duration
1871877 954     7       1       0       0       0
1871877 955     7       2       1       2       1
1871877 956     3       1       1       4       1
1871877 957     6       0       1       1       1
1871877 958     7       1       1       6       3
1871877 959     7       1       0       0       0
1871877 960     7       1       0       0       0
1871877 961     7       0       1       1       1
1871877 962     7       2       1       5       1
1871877 963     4       1       1       4       3
1871877 964     2       1       0       0       0
1871877 964     7       1       0       0       0

I just wanto count how long the customer stay in the switched shopping
type.  Could any one give some suggestion of how to constuct the
variable "Duration"?
The one above is make manually.

Thanks a lot!

Albert

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