Presto和hive分区发现(Presto and hive partition discovery)

 看看df的结构（ str ）你可以看到它自己作为data.frame。 
 
> str(df)
'data.frame':   10 obs. of  2 variables:
 $ foo: Factor w/ 2 levels "ab","ac": 1 1 1 1 1 2 2 2 2 2
 $ boo:'data.frame':    10 obs. of  2 variables:
  ..$ X1: Factor w/ 1 level "a": 1 1 1 1 1 1 1 1 1 1
  ..$ X2: Factor w/ 2 levels "b","c": 1 1 1 1 1 2 2 2 2 2
 
 因此你可以通过df$boo$X1和df$boo$X1访问它们 
 
 如果你想附加boo列，你可以使用cbind ，如下所示： 
 
df <- data.frame('foo' = rep(c('ab','ac'), each = 5))
df <- cbind(df, do.call('rbind', strsplit(as.character(df$foo),'',fixed=FALSE)))
names(df) <- c("foo", "boo_1", "boo_2")
 
 给你的 
 
   foo boo_1 boo_2
1   ab     a     b
2   ab     a     b
3   ab     a     b
4   ab     a     b
5   ab     a     b
6   ac     a     c
7   ac     a     c
8   ac     a     c
9   ac     a     c
10  ac     a     c

Having a look at the structure (str) of df you can see that boo itsself as a data.frame.
 
> str(df)
'data.frame':   10 obs. of  2 variables:
 $ foo: Factor w/ 2 levels "ab","ac": 1 1 1 1 1 2 2 2 2 2
 $ boo:'data.frame':    10 obs. of  2 variables:
  ..$ X1: Factor w/ 1 level "a": 1 1 1 1 1 1 1 1 1 1
  ..$ X2: Factor w/ 2 levels "b","c": 1 1 1 1 1 2 2 2 2 2
 
So you can access them by df$boo$X1 and df$boo$X1
 
if you want to append the boo columns you can use cbind as follows:
 
df <- data.frame('foo' = rep(c('ab','ac'), each = 5))
df <- cbind(df, do.call('rbind', strsplit(as.character(df$foo),'',fixed=FALSE)))
names(df) <- c("foo", "boo_1", "boo_2")
 
which gives you
 
   foo boo_1 boo_2
1   ab     a     b
2   ab     a     b
3   ab     a     b
4   ab     a     b
5   ab     a     b
6   ac     a     c
7   ac     a     c
8   ac     a     c
9   ac     a     c
10  ac     a     c