Stata 15 help for obs
[D] obs  Increase the number of observations in a dataset
Syntax
set obs #
Description
set obs changes the number of observations in the current dataset. #
must be at least as large as the current number of observations. If
there are variables in memory, the values of all new observations are set
to missing.
Examples
. drop _all (drop data from memory)
. set obs 100 (make 100 observations)
. gen x = _n (x = 1, 2, 3, .., 100)
. gen y = x^2 (y = 1, 4, 9, .., 10000)
. scatter y x (make a graph)
