Vector creation with c() in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the c() function do in R?

The c() function combines values into a vector, which is a basic data structure in R that holds elements of the same type.

beginner

How do you create a numeric vector with the numbers 1, 2, and 3 using c()?

You write c(1, 2, 3). This creates a vector containing the numbers 1, 2, and 3.

intermediate

Can c() combine different types like numbers and characters in one vector?

Yes, but R will convert all elements to the most flexible type to keep the vector consistent. For example, combining numbers and characters will convert numbers to characters.

beginner

What happens if you use c() with no arguments?

It creates an empty vector with no elements.

intermediate

How does c() differ from other vector creation functions like seq() or rep()?

c() combines specific values you list, while seq() creates sequences of numbers and rep() repeats values. c() is for manual combination.

What does c(4, 5, 6) create in R?

A A vector with elements 4, 5, and 6

B A list with elements 4, 5, and 6

C A matrix with elements 4, 5, and 6

D An error because of missing quotes

c() creates a vector combining the values 4, 5, and 6.

What type will the vector c(1, "a", TRUE) have?

A Mixed types allowed

B Numeric

C Logical

D Character

R converts all elements to character because it is the most flexible type among numeric, logical, and character.

What is the result of c() with no arguments?

A An empty vector

B An error

C A vector with one NA

D NULL

Calling c() without arguments returns an empty vector.

Which function is best to create a vector repeating the number 3 five times?

A c(3, 3, 3, 3, 3)

B rep(3, 5)

C seq(3, 5)

D c(3:5)

rep(3, 5) repeats the number 3 five times efficiently.

If you want to combine the numbers 1, 2, and 3 into a vector, which is correct?

A combine(1, 2, 3)

B vector(1, 2, 3)

C c(1, 2, 3)

D seq(1, 3)

c(1, 2, 3) is the correct way to combine values into a vector.

Explain how the c() function works to create vectors in R.

Think about how you put things together in a row.

Describe what happens when you mix numbers and characters inside c().

Consider how R keeps things consistent.

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