List
A list is a generic vector containing other objects.
For example, the following variable x is a list containing copies of three vectors n, s, b, and a numeric value 3.
> n = c(2, 3, 5)
> s = c("aa", "bb", "cc", "dd", "ee")
> b = c(TRUE, FALSE, TRUE, FALSE, FALSE)
> x = list(n, s, b, 3) # x contains copies of n, s, b
> s = c("aa", "bb", "cc", "dd", "ee")
> b = c(TRUE, FALSE, TRUE, FALSE, FALSE)
> x = list(n, s, b, 3) # x contains copies of n, s, b
List Slicing
We retrieve a list slice with the single square bracket "[]" operator. The following is a slice containing the second member of x, which is a copy of s.
With an index vector, we can retrieve a slice with multiple members. Here a slice containing the second and fourth members of x.
Member Reference
In order to reference a list member directly, we have to use the double square bracket "[[]]" operator. The following object x[[2]] is the second member of x. In other words, x[[2]] is a copy of s, but is not a slice containing s or its copy.
We can modify its content directly.
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