Named vectors in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a named vector in R?

A named vector in R is a vector where each element has a name attached to it. These names help identify elements by name instead of just by position.

beginner

How do you assign names to a vector in R?

You can assign names to a vector using the names() function. For example: names(x) <- c('a', 'b', 'c') assigns names 'a', 'b', and 'c' to the elements of vector x.

beginner

How can you access elements of a named vector by name?

You can access elements by using the name inside square brackets. For example, if x is a named vector, x['name'] returns the element with the name 'name'.

intermediate

What happens if you assign duplicate names to elements in a named vector?

If you assign duplicate names, R allows it but accessing by name returns all elements with that name. This can cause confusion, so unique names are recommended.

beginner

How do you remove names from a named vector?

You can remove names by setting them to NULL using names(x) <- NULL. This makes the vector unnamed again.

Which function is used to assign names to a vector in R?

A names()

B colnames()

C rownames()

D dimnames()

The names() function is used to assign or get names of vector elements.

How do you access the element named 'age' in a named vector v?

A v[age]

B v$age

C v['age']

D v.age

You access named vector elements using square brackets and the name as a string: v['age'].

What will names(c(10, 20, 30)) return if no names are assigned?

A c('', '', '')

B c('10', '20', '30')

C An error

D NULL

If no names are assigned, names() returns NULL.

If a named vector has duplicate names, what happens when you access by that name?

A Returns only the first element with that name

B Returns all elements with that name

C Returns NULL

D Throws an error

Accessing by a duplicate name returns all elements with that name.

How do you remove all names from a named vector x?

A Both C and D

B names(x) <- ''

C x <- unname(x)

D names(x) <- NULL

You can remove names by setting names(x) <- NULL or by using unname(x).

Explain what a named vector is and how it can be useful in R programming.

Think about how names act like labels on elements.

Describe how to assign, access, and remove names from a vector in R.

Focus on the names() function and indexing.

Practice

1. What is a named vector in R?

easy

A. A vector that only contains numeric values

B. A vector where each element has a name label for easy access

C. A vector that cannot be modified after creation

D. A vector that stores only character strings

Solution

1. Step 1: Understand vector naming

   Named vectors have names assigned to each element, making it easier to access elements by name.

2. Step 2: Compare options

   Only A vector where each element has a name label for easy access correctly describes a named vector as having name labels for elements.

3. Final Answer:

   A vector where each element has a name label for easy access -> Option B

4. Quick Check:

   Named vector = vector with names [OK]

Hint: Named vectors have labels for elements, not just values [OK]

Common Mistakes:

• Thinking named vectors only hold numbers
• Confusing named vectors with immutable vectors
• Assuming named vectors store only strings

2. Which of the following is the correct way to create a named vector in R?

easy

A. c(apple = 5, banana = 3, cherry = 7)

B. vector(apple:5, banana:3, cherry:7)

C. named_vector(5, 3, 7, names = c('apple', 'banana', 'cherry'))

D. c(5 = apple, 3 = banana, 7 = cherry)

Solution

1. Step 1: Recall named vector syntax

   Named vectors are created using c(name = value) pairs.

2. Step 2: Check each option

   c(apple = 5, banana = 3, cherry = 7) uses correct syntax: c(apple = 5, banana = 3, cherry = 7). Others use invalid syntax or functions.

3. Final Answer:

   c(apple = 5, banana = 3, cherry = 7) -> Option A

4. Quick Check:

   Use c(name = value) to create named vectors [OK]

Hint: Use c(name = value) pairs to create named vectors [OK]

Common Mistakes:

• Using colons instead of equals for naming
• Trying to use non-existent functions like named_vector()
• Placing values before names incorrectly

3. What will be the output of the following R code?

fruits <- c(apple = 10, banana = 5, cherry = 8)
fruits["banana"]

medium

A. 5

B. "banana"

C. Error: object not found

D. c(banana = 5)

Solution

1. Step 1: Understand named vector indexing

   Accessing a named vector element by name returns a named vector of length 1 with that element.

2. Step 2: Analyze the code output

   fruits["banana"] returns a named vector with name 'banana' and value 5, shown as c(banana = 5).

3. Final Answer:

   c(banana = 5) -> Option D

4. Quick Check:

   Access by name returns named vector element [OK]

Hint: Accessing by name returns named vector element, not just value [OK]

Common Mistakes:

• Expecting just the value without name
• Confusing output with string name
• Assuming it causes an error

4. Identify the error in the following R code that tries to create a named vector:

numbers <- c(1 = "one", 2 = "two", 3 = "three")

medium

A. Values and names are reversed; names should be strings on the left

B. The syntax uses numbers as names incorrectly; names must be on the left side

C. Numbers cannot be used as names in named vectors

D. The c() function cannot create named vectors

Solution

1. Step 1: Check named vector syntax

   Named vectors use name = value pairs, with names on the left and values on the right.

2. Step 2: Analyze the code

   The code uses numbers on the left and strings on the right, which reverses the expected order.

3. Final Answer:

   Values and names are reversed; names should be strings on the left -> Option A

4. Quick Check:

   Names = values, not values = names [OK]

Hint: Names must be on left side, values on right in c(name = value) [OK]

Common Mistakes:

• Putting values on left and names on right
• Thinking numbers cannot be names (they can as strings)
• Believing c() can't create named vectors

5. Given the named vector temps <- c(Mon = 22, Tue = 25, Wed = 20, Thu = 23), how would you create a new named vector with only days where temperature is above 22?

hard

A. temps[">22"]

B. temps[temps < 22]

C. temps[temps > 22]

D. temps[temps == 22]

Solution

1. Step 1: Understand logical indexing with named vectors

   You can use a logical condition inside square brackets to filter elements.

2. Step 2: Apply condition temps > 22

   temps > 22 returns TRUE for days with temperature above 22, so temps[temps > 22] selects those days.

3. Final Answer:

   temps[temps > 22] -> Option C

4. Quick Check:

   Use logical condition inside brackets to filter named vectors [OK]

Hint: Use temps[temps > value] to filter named vectors by condition [OK]

Common Mistakes:

• Using incorrect comparison operators
• Trying to index by string '>22' which is invalid
• Selecting equal or less than values instead of greater