In jr-packages/jrPredictive: Jumping Rivers: Machine Learning with R

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)

jr-packages/jrPredictive documentation built on Oct. 12, 2020, 11:44 a.m.