In [14]:
cohorts=cohorts.reset_index()
cohorts.head()
Out[14]:
FirstOrder OrderPeriod UserId
0 2009-01 2009-01 22
1 2009-01 2009-02 8
2 2009-01 2009-03 10
3 2009-01 2009-04 9
4 2009-01 2009-05 10