Is there a way to transform data in Stata from a single observation (e.g. # of patients experiencing an event) into many observations?

I'm trying to efficiently use Stata to estimate standard errors around a proportion of patients experiencing an adverse event in a model we are adapting. An example dataset:

n = 74

a = 56

b = 18

Where n is the number of patients, a is the number of patients experiencing an event and b is the number not experiencing an event.

When the data is in this format, I note that using

ratio myratio: a/n

Returns a proportion (a/n) but does not estimate a linearized standard error. Manually converting the data into "long" format however fixes this issue. Long format being:

No. observations = n (74)

n = 1 for all observations

a = 1 if index <= 18 else 0

b = 1 if index > 18 else 0

It's been a while since I have used Stata, is there a quick way to do this? I can't even remember how to extend the length of the dataset to the number of samples N!

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