<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _collect_state_names(self, variable):
        "Return a list of states that the variable takes in the data"
        states = sorted(list(self.data.ix[:, variable].dropna().unique()))
        return states