Not all datasets have an id number variable (for example, if you have performed an anonymous survey, there might not have been a need to mark the questionnaires with any id number). This is easily fixed in Stata.
gen varname = _n |
For example:
gen id = _n |
| Note Stata will assign numbers in the order that the dataset is sorted, so make sure that you have it sorted in the way you like first. |
More informationhelp generatehelp sort |