      a     b c    
  <dbl> <int> <lgl>
1   1       1 TRUE 
2   2.5     2 FALSE
3  NA      NA NA   
  d     e    
  <chr> <fct>
1 a     a    
2 b     b    
3 <NA>  <NA> 
  f         
  <date>    
1 2015-12-10
2 2015-12-11
3 NA        
  g                 
  <dttm>            
1 2015-12-09 10:51:…
2 2015-12-09 10:51:…
3 NA                
  h        
  <list>   
1 <int [1]>
2 <int [1]>
3 <int [1]>
  i         
  <list>    
1 <list [2]>
2 <list [1]>
3 <list [1]>
