      a     b c     d     e      f         
  <dbl> <int> <lgl> <chr> <fctr> <date>    
1  1.00     1 T     a     a      2015-12-10
2  2.50     2 F     b     b      2015-12-11
3 NA       NA NA    <NA>  <NA>   NA        
  g                   h         i         
  <dttm>              <list>    <list>    
1 2015-12-09 10:51:35 <int [1]> <list [2]>
2 2015-12-09 10:51:36 <int [1]> <list [1]>
3 NA                  <int [1]> <list [1]>
