firm_id date ret
10001 11/30/2015 -0.00907
10001 12/31/2015 -0.13215
10001 01/29/2015 0.116779
10001 02/29/2015 -0.05529
10001 03/31/2015 -0.00636
10001 04/29/2015 -0.0557
10001 05/31/2015 -0.02192
10001 06/30/2015 -0.02101
10001 07/29/2015 0.026466
10001 08/31/2015 0.03662
10001 09/30/2015 0.04212
10001 10/31/2016 0.619948
10001 11/30/2016 0.012146
10001 12/30/2016 0.01
10002 01/31/3016 0.05
10002 02/28/2016 0.139785
10002 03/31/2016 0.070755
10002 04/30/2016 0.052863
10002 05/30/2016 -0.02092
10002 06/30/2016 -0.13248
10002 07/31/2016 0.049261
10002 08/29/2016 0
10002 09/30/2016 0.070423
10002 10/31/2016 -0.0614
10002 11/28/2016 0
10002 12/31/2016 -0.07477
10002 01/30/2017 0.09596
10002 02/27/2017 -0.01382
How do I go from mothly to annualy returns in stat ? Thank you