Named list elements in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a named list element in R?

A named list element is a part of a list that has a name assigned to it, allowing you to access it by name instead of by position.

beginner

How do you create a named list element in R?

You create a named list element by using the syntax list(name = value), where name is the element's name and value is its content.

beginner

How do you access a named list element in R?

You access a named list element using the dollar sign $ followed by the element's name, like mylist$name, or by using double square brackets with the name as a string, like mylist[["name"]].

intermediate

What happens if you try to access a named list element that does not exist?

If you try to access a named list element that does not exist, R returns NULL without an error.

intermediate

Can named list elements have names that are not valid variable names? How do you access them?

Yes, named list elements can have names with spaces or special characters. You access them using double square brackets and quotes, like mylist[["my name"]].

How do you create a named list element called 'age' with value 30 in R?

A list(age: 30)

B list(30 = age)

C list(age = 30)

D list('age', 30)

The correct syntax is list(age = 30) to create a named element 'age' with value 30.

Which of these accesses the named element 'name' from a list called mylist?

A mylist$name

B mylist[name]

C mylist[[name]]

D mylist$name()

Use mylist$name or mylist[["name"]] to access named elements. Option B returns a sublist, not the element.

What does R return if you access a non-existent named list element?

A Error

B NULL

C NA

D 0

R returns NULL when a named list element does not exist.

How do you access a named list element with a space in its name, like 'my name'?

A mylist[my name]

B mylist$my name

C mylist$'my name'

D mylist[['my name']]

Use double square brackets with quotes: mylist[['my name']].

Which is a correct way to create a list with two named elements 'x' and 'y'?

A list(x = 1, y = 2)

B list(1 = x, 2 = y)

C list('x', 1, 'y', 2)

D list(x:1, y:2)

The correct syntax is list(x = 1, y = 2).

Explain how to create and access named list elements in R.

Think about how you give names and then get values by those names.

What happens when you try to access a named list element that does not exist? How can you handle it?

Consider what R returns and how to avoid errors.