st: Generating distinct observations after expand

[Stefan Bernhard <stefanbernhard88@gmail.com>]

Suppose there are an arbitrary number of dummy variables and n
identical observations (after expand) for a number of individuals,
where n can be different for each individual.

I want to end up with n distinct observations per individual, where
each observation has exactly one of the dummies with initial value 1
kept at 1, while all others are set to 0, and the set of dummies must
uniquely identify all observations within each individual.

e.g.

id | d1 d2 d3 d4
1 | 1 0 1 0
1 | 1 0 1 0
2 | 1 0 0 1
2 | 1 0 0 1
3 | 1 1 0 1
3 | 1 1 0 1
3 | 1 1 0 1

I want to end up with

id | d1 d2 d3 d4
1 | 1 0 0 0
1 | 0 0 1 0
2 | 1 0 0 0
2 | 0 0 0 1
3 | 1 0 0 0
3 | 0 1 0 0
3 | 0 0 0 1

I have been trying around with while, foreach, macros, by: and whatnot
for an hour now and can't find a way to do that.

thanks, stefan bernhard,
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