NA float format bug
Need to put a leading space on NaN by default...I will fix this weekend if no one else gets to it @adamklein 

```
       D        E         F      
count  3.00000  3.000000  3.00000
mean   0.45674  0.522317  0.15975
std    1.41366  1.268866  0.95044
min   -1.02552 -0.414997 -0.77343
25%   -0.20989 -0.199634 -0.32366
50%    0.60573  0.015730  0.12611
75%    1.19786  0.990974  0.62634
max    1.78999  1.966219  1.12657
count  1.00000  1.000000  1.00000
mean  -1.17800 -0.124118  0.19188
std   NaN      NaN       NaN     
min   -1.17800 -0.124118  0.19188
25%   -1.17800 -0.124118  0.19188
50%   -1.17800 -0.124118  0.19188
75%   -1.17800 -0.124118  0.19188
max   -1.17800 -0.124118  0.19188
count  4.00000  4.000000  4.00000
mean  -0.09697 -0.723308  0.18293
std    1.07386  0.870480  0.39080
min   -1.07445 -1.923554 -0.15451
25%   -0.55308 -1.080760 -0.03626
50%   -0.37468 -0.480612  0.07309
75%    0.08143 -0.123160  0.29228
max    1.43593 -0.008454  0.74007
count  3.00000  3.000000  3.00000
mean   0.39914 -0.110401 -0.82227
std    0.22223  1.146990  1.42853
min    0.17519 -1.022600 -1.78633
25%    0.28890 -0.754235 -1.64286
50%    0.40260 -0.485871 -1.49940
75%    0.51111  0.345698 -0.34025
max    0.61961  1.177267  0.81891
```
