Named vectors in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of named vector indexing

What is the output of this R code snippet?

R Programming

vec <- c(a = 10, b = 20, c = 30)
result <- vec["b"]
print(result)

A c 30

B b 20

C 20

D Error: object 'b' not found

💡 Hint

Remember that named vectors keep their names when indexed by name.

Indexing a named vector by name returns a named vector of length 1, so the output includes the name and the value.

❓ Predict Output

intermediate

Length of named vector after subsetting

What is the length of the vector after this operation?

R Programming

vec <- c(x = 5, y = 15, z = 25)
sub_vec <- vec[c("x", "z")]
length(sub_vec)

A 1

B 3

C 2

D Error: invalid subscript type

💡 Hint

Subsetting by a vector of names returns those elements.

Subsetting by two names returns a vector of length 2 containing those elements.

❓ Predict Output

advanced

Output of modifying named vector elements

What is the output of this code?

R Programming

vec <- c(a = 1, b = 2, c = 3)
vec["b"] <- 10
print(vec)

A

a 1
b 10
c 3

B 1 10 3

C

a 1
b 2
c 3

D Error: cannot assign to a named vector element

💡 Hint

You can assign new values to named vector elements by name.

Assigning to a named element changes its value but keeps the name.

❓ Predict Output

advanced

Result of unnamed indexing on named vector

What will this code print?

R Programming

vec <- c(one = 100, two = 200, three = 300)
print(vec[2])

A one 100

B 200

C Error: subscript out of bounds

D two 200

💡 Hint

Indexing by position returns a named vector element.

Indexing by position returns the element with its name.

❓ Predict Output

expert

Output of combining named vectors with overlapping names

What is the output of this R code?

R Programming

v1 <- c(a = 1, b = 2)
v2 <- c(b = 3, c = 4)
combined <- c(v1, v2)
print(combined)

A

a 1
b 2
b 3
c 4

B

a 1
b 5
c 4

C

a 1
b 3
c 4

D Error: duplicate names not allowed

💡 Hint

Combining vectors concatenates elements and keeps all names, even duplicates.

Concatenating named vectors keeps all elements and names, including duplicates.

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