cohorts.loc[cohorts.shape[0],'FirstOrder']='2009-02'
cohorts.loc[cohorts.shape[0]-1,'OrderPeriod']='2010-03'
cohorts.loc[cohorts.shape[0]-1,'TotalUsers']=0
cohorts.sort_values(['FirstOrder','OrderPeriod'],inplace=True)
cohorts[cohorts['FirstOrder']=='2009-02']