An R list is an object consisting of an ordered collection of (possibly
different) objects known as its components. For example, a list could consist of
a numeric vector and a data frame. To create a list, we use the list
function
lst = list(name = "Fred", wife = "Mary", children = 3, child.ages = c(4, 7, 9))
Components are always numbered. In the lst
object above, we can access
individual components using the double bracket notation. For example to select
the fourth element from the list, we have
lst[[4]]
So to access the first element of the fourth component we do
lst[[4]][1]
The length
function gives the number of top level components:
length(lst)
Components of lists may also be named. If this is the case, then we can also access the element using its name:
lst[["wife"]] lst$name
A useful function for interrogating an object is
str
. Using the lst
object
as an example, we have
str(lst)
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