> d <- data.frame(name=c("李明", "张聪", "王建"), age=c(30, 35, 28),   height=c(180, 162, 175)) 
> typeof(d)    
[1] "list" 
 
 >  n = c(2, 3, 5)     
>  s = c("aa", "bb", "cc")     
>  b = c(TRUE, FALSE, TRUE)     
>  df = data.frame(n, s, b)   
> typeof(df)    
[1] "list"
 
 
df <- data.frame(a=1:2, b=letters[1:2]);   
> str(df)    
'data.frame':   2 obs. of  2 variables:    
 $ a: int  1 2    
 $ b: Factor w/ 2 levels "a","b": 1 2    
> class(df);    
[1] "data.frame"    
> mode(df);    
[1] "list"    
> typeof(df);    
[1] "list"