'[' - Extract or Replace

• '[' works on lists, and always returns a list

y <- list(a = 1:10,
          b = 11:20)

y[c(1,2)]

## $a
##  [1]  1  2  3  4  5  6  7  8  9 10
## 
## $b
##  [1] 11 12 13 14 15 16 17 18 19 20