Selecting single elem. with [[ and $

List example:

x <- list(apple = c(10, 15), banana = c(20, 25), melon = c(30, 35))
str(x)

## List of 3
##  $ apple : num [1:2] 10 15
##  $ banana: num [1:2] 20 25
##  $ melon : num [1:2] 30 35

x$melon

## [1] 30 35

x[3]

## $melon
## [1] 30 35

x[[3]]

## [1] 30 35

x["melon"]

## $melon
## [1] 30 35

x[["melon"]]

## [1] 30 35