Vector creation with c() in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of combining different types with c()

What is the output of this R code?

x <- c(1, TRUE, "3", 4.5)
print(x)

R Programming

x <- c(1, TRUE, "3", 4.5)
print(x)

A [1] 1 1 3 4.5

B [1] "1" "TRUE" "3" "4.5"

C [1] "1" "1" "3" "4.5"

D [1] 1 TRUE "3" 4.5

💡 Hint

Remember that c() converts all elements to the most flexible type to keep them in one vector.

In R, when combining different types with c(), all elements are coerced to a common type. Here, numeric and logical values are converted to character because of the presence of a character "3". TRUE becomes "TRUE" as character.

❓ Predict Output

intermediate

Length of vector created with c()

What is the length of the vector created by this code?

v <- c(NA, NULL, 5, c(2, 3))
length(v)

R Programming

v <- c(NA, NULL, 5, c(2, 3))
length(v)

A 5

B 2

C 3

D 4

💡 Hint

Remember that NULL is ignored inside c(), but NA counts as an element.

NULL is dropped when combined with c(), so the vector is c(NA, 5, 2, 3) which has length 4.

🔧 Debug

advanced

Why does this c() call produce an error?

This code produces an error. What is the cause?

v <- c(1, 2, 3, , 5)

R Programming

v <- c(1, 2, 3, , 5)

A Syntax error due to missing value between commas

B No error, code runs fine

C Runtime error because c() cannot handle more than 4 elements

D Type error because 5 is not compatible with previous numbers

💡 Hint

Check the commas carefully inside the c() function.

There is a missing value between two commas, which is a syntax error in R.

🧠 Conceptual

advanced

Behavior of c() with named elements

What is the output of this R code?

v <- c(a=1, b=2, 3)
names(v)

R Programming

v <- c(a=1, b=2, 3)
names(v)

A [1] "a" "b" "3"

B [1] "a" "b" "c"

C [1] "a" "b" ""

D [1] NULL

💡 Hint

Only elements explicitly named get names; unnamed elements have empty names.

The first two elements have names "a" and "b". The third element is unnamed, so its name is an empty string "".

❓ Predict Output

expert

Output of nested c() calls with mixed types

What is the output of this R code?

v <- c(1, c(TRUE, "text"), 3.5)
print(v)

R Programming

v <- c(1, c(TRUE, "text"), 3.5)
print(v)

A [1] "1" "TRUE" "text" "3.5"

B [1] 1 1 "text" 3.5

C [1] "1" "1" "text" "3.5"

D [1] 1 TRUE "text" 3.5

💡 Hint

Remember that c() flattens nested vectors and coerces types to the most flexible one.

The inner c(TRUE, "text") coerces TRUE to character "TRUE". Then the outer c() flattens and coerces all to character because of "text". 1 becomes "1", 3.5 becomes "3.5", "TRUE" and "text" remain.

Practice

1. What does the c() function do in R?

easy

A. Reads data from a file

B. Creates a matrix

C. Combines values into a vector

D. Deletes variables

Solution

1. Step 1: Understand the purpose of c()

   The c() function is used to combine multiple values into a single vector in R.

2. Step 2: Compare with other options

   Creating a matrix, deleting variables, or reading files are done by other functions, not c().

3. Final Answer:

   Combines values into a vector -> Option C

4. Quick Check:

   c() = combine values [OK]

Hint: Remember: c() means combine values into one vector [OK]

Common Mistakes:

• Thinking c() creates matrices
• Confusing c() with file reading functions
• Assuming c() deletes variables

2. Which of the following is the correct syntax to create a numeric vector with values 1, 2, and 3 in R?

easy

A. vector(1, 2, 3)

B. c(1, 2, 3)

C. c[1, 2, 3]

D. combine(1, 2, 3)

Solution

1. Step 1: Recall the syntax for vector creation

   In R, c() is used to combine values into a vector, so c(1, 2, 3) is correct.

2. Step 2: Identify incorrect syntax

   vector() is a different function needing length/type, c[] is invalid syntax, and combine() is not an R function.

3. Final Answer:

   c(1, 2, 3) -> Option B

4. Quick Check:

   Correct vector syntax = c(1, 2, 3) [OK]

Hint: Use parentheses with c(), not brackets or other words [OK]

Common Mistakes:

• Using square brackets [] instead of parentheses ()
• Using vector() without proper arguments
• Trying non-existent functions like combine()

3. What is the output of the following R code?

vec <- c(5, 10, 15)
print(vec[2])

medium

A. 10

B. 5

C. 15

D. Error

Solution

1. Step 1: Understand vector indexing in R

   R vectors are 1-indexed, so vec[2] accesses the second element.

2. Step 2: Identify the second element in the vector

   The vector is c(5, 10, 15), so the second element is 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Second element of c(5,10,15) = 10 [OK]

Hint: Remember R starts counting at 1, not 0 [OK]

Common Mistakes:

• Assuming indexing starts at 0
• Confusing element positions
• Expecting an error from valid indexing

4. Identify the error in this R code:

my_vec <- c(1, 2, 3
print(my_vec)

medium

A. Missing closing parenthesis in c()

B. Using print() incorrectly

C. Vector cannot contain numbers

D. Variable name is invalid

Solution

1. Step 1: Check the syntax of c()

   The c() function call is missing a closing parenthesis after the numbers.

2. Step 2: Verify other parts of the code

   The print() function and variable name are correct, and vectors can contain numbers.

3. Final Answer:

   Missing closing parenthesis in c() -> Option A

4. Quick Check:

   Syntax error due to missing ')' [OK]

Hint: Count your parentheses carefully [OK]

Common Mistakes:

• Forgetting to close parentheses
• Thinking print() is wrong
• Believing vectors can't hold numbers

5. You want to create a vector of mixed types: numbers and text, using c(). Which code correctly creates a vector with 10, "apple", and TRUE?

hard

A. c(10 + "apple" + TRUE)

B. c(10; "apple"; TRUE)

C. c(10 "apple" TRUE)

D. c(10, "apple", TRUE)

Solution

1. Step 1: Understand how c() handles mixed types

   The c() function can combine numbers, text, and logical values into a vector, coercing to a common type if needed.

2. Step 2: Check syntax correctness

   c(10, "apple", TRUE) uses commas to separate values correctly. Options A, B, and D use invalid separators or operators.

3. Final Answer:

   c(10, "apple", TRUE) -> Option D

4. Quick Check:

   Correct mixed vector syntax uses commas [OK]

Hint: Separate items with commas inside c() [OK]

Common Mistakes:

• Using semicolons instead of commas
• Trying to add different types with +
• Omitting commas between values