To identify unique values of variables in Stata one option is to use the levelsof command. From the Stata documentation:
levelsof serves two different functions. First, it gives a compact display of the distinct values of varname. More commonly, it is useful when you desire to cycle through the distinct values of varname with (say) foreach; see [P] foreach. levelsof leaves behind a list in r(levels) that may be used in a subsequent command.
In other words when running the command in its most basic form it generates a list that can be used as needed.
sysuse nlsw88, clear
levelsof occupation
display "`r(levels)'"Here we run the levelsof command on the occupation variable and then we display the generated list. There is also the option to store the values in a local macro:
levelsof occupation, local(occ_lvls)
display "`occ_lvls'"One limitation of the levelsof command is that it can only handle one variable at a time. In order to handle multiple variables at once and can identify unique combinations of observations based on that there are other options which we’ll explore in another post.