index   date        username    count
0       2015-11-01  1           16
1       2015-11-01  2           1
2       2015-11-01  3           1
3       2015-10-01  1           2
4       2015-10-01  4           29
5       2015-10-01  5           1
6       2014-09-01  1           3
7       2014-09-01  3           1
8       2014-09-01  4           1

index   date        mean
0       2015-11-01  6
1       2015-10-01  10.7
2       2014-09-01  1.3