Special operators (%in%, %*%) in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if 3 is in the vector.

R Programming

3 [1] c(1, 2, 3, 4, 5)

Drag options to blanks, or click blank then click option'

A%in%

B%*%

C%/%

D%%

Attempts:

3 left

💡 Hint

Common Mistakes

Using %*% which is for matrix multiplication.

Using %% which is for modulo operation.

The %in% operator checks if the left value is present in the right vector.

2fill in blank

medium

Complete the code to multiply two matrices A and B.

R Programming

result <- A [1] B

Drag options to blanks, or click blank then click option'

A%in%

B%%

C%*%

D%/%

Attempts:

3 left

💡 Hint

Common Mistakes

Using %in% which checks membership, not multiplication.

Using %% which is modulo, not multiplication.

The %*% operator performs matrix multiplication in R.

3fill in blank

hard

Fix the error in the code to check if 'apple' is in the fruits vector.

R Programming

'apple' [1] fruits

Drag options to blanks, or click blank then click option'

A%*%

Bis.in

Cin

D%in%

Attempts:

3 left

💡 Hint

Common Mistakes

Using %*% which is matrix multiplication.

Using 'in' without percent signs which is not valid syntax.

The correct operator to check membership is %in%. Other options are invalid in R.

4fill in blank

hard

Fill both blanks to create a named vector with lengths of words longer than 3 characters.

R Programming

lengths <- c([1] = [2] for word in words if nchar(word) > 3)

Drag options to blanks, or click blank then click option'

Aword

Bnchar(word)

Clength(word)

Dcount(word)

Attempts:

3 left

💡 Hint

Common Mistakes

Using length(word) which returns 1 for strings.

Using count(word) which is not a base R function.

The names of the vector elements should be the words themselves, and the values should be their character counts using nchar().

5fill in blank

hard

Fill all three blanks to create a named vector of word lengths for words longer than 4 characters.

R Programming

word_lengths <- c([1] = [2] for word in words if nchar(word) [3] 4)

Drag options to blanks, or click blank then click option'

Aword

Bnchar(word)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Using length(word) instead of nchar(word).

The vector names are the words, values are their lengths using nchar(), and the condition checks if length is greater than 4.

Practice

1. What does the %in% operator do in R?

easy

A. Calculates the sum of two vectors

B. Performs element-wise multiplication of two vectors

C. Performs matrix multiplication

D. Checks if elements of one vector are present in another vector

Solution

1. Step 1: Understand the purpose of %in%

   The %in% operator is used to check membership, meaning it tests if elements of one vector exist in another.

2. Step 2: Compare with other operations

   Other options describe arithmetic or matrix operations, which are not the function of %in%.

3. Final Answer:

   Checks if elements of one vector are present in another vector -> Option D

4. Quick Check:

   %in% = membership check [OK]

Hint: Remember: %in% means 'is in' for membership [OK]

Common Mistakes:

• Confusing %in% with arithmetic operators
• Thinking %in% does matrix multiplication
• Assuming %in% returns numeric results

2. Which of the following is the correct syntax for matrix multiplication in R?

easy

A. A * B

B. A %*% B

C. A %in% B

D. A + B

Solution

1. Step 1: Identify matrix multiplication operator

   In R, matrix multiplication is done using %*%, so A %*% B is correct syntax.

2. Step 2: Differentiate from other operators

   * is element-wise multiplication, %in% is membership, and + is addition.

3. Final Answer:

   A %*% B -> Option B

4. Quick Check:

   Matrix multiply = %*% [OK]

Hint: Use %*% for matrix multiply, * for element-wise [OK]

Common Mistakes:

• Using * instead of %*% for matrix multiplication
• Confusing %in% with multiplication
• Using + for multiplication

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

x <- c(3, 1, 5)
y <- c(3, 4, 5, 6)
x %in% y

medium

A. [TRUE, FALSE, TRUE]

B. [FALSE, TRUE, FALSE]

C. [TRUE, TRUE, TRUE]

D. [FALSE, FALSE, FALSE]

Solution

1. Step 1: Check each element of x in y

   3 is in y, so TRUE; 1 is not in y, so FALSE; 5 is in y, TRUE.

2. Step 2: Form the logical vector

   The result is [TRUE, FALSE, TRUE].

3. Final Answer:

   [TRUE, FALSE, TRUE] -> Option A

4. Quick Check:

   %in% returns logical vector [OK]

Hint: Check each element presence one by one [OK]

Common Mistakes:

• Mixing order of TRUE/FALSE in output
• Assuming %in% returns indices
• Confusing %in% with element-wise comparison

4. Identify the error in the following R code:

A <- matrix(c(1,2,3,4), nrow=2)
B <- matrix(c(5,6,7,8), nrow=2)
C <- A *%* B

medium

A. Matrices A and B have incompatible dimensions

B. Missing library for matrix multiplication

C. Incorrect operator *%* used for matrix multiplication

D. Matrix A is not defined properly

Solution

1. Step 1: Check operator syntax

   The operator *%* is invalid in R; correct operator is %*%.

2. Step 2: Verify matrix dimensions and definitions

   Both matrices are 2x2, so dimensions are compatible and matrices are defined correctly.

3. Final Answer:

   Incorrect operator *%* used for matrix multiplication -> Option C

4. Quick Check:

   Matrix multiply operator is %*% [OK]

Hint: Use %*% exactly for matrix multiplication [OK]

Common Mistakes:

• Typing operators in wrong order
• Assuming *%* is valid
• Confusing element-wise * with matrix multiply

5. Given two matrices:

M1 <- matrix(c(1, 0, 2, 3), nrow=2)
M2 <- matrix(c(4, 1, 0, 2), nrow=2)

Which R expression correctly computes the matrix product and then checks if the number 5 is in the resulting matrix?

hard

A. 5 %in% (M1 %*% M2)

B. M1 *%*% M2 %in% 5

C. M1 %in% 5 %*% M2

D. M1 %*% M2 == 5

Solution

1. Step 1: Perform matrix multiplication correctly

   Use %*% to multiply M1 and M2: M1 %*% M2.

2. Step 2: Check membership of 5 in the product matrix

   Use %in% to check if 5 is present in the resulting matrix: 5 %in% (M1 %*% M2).

3. Final Answer:

   5 %in% (M1 %*% M2) -> Option A

4. Quick Check:

   Matrix multiply then membership check = 5 %in% (M1 %*% M2) [OK]

Hint: Chain %*% then %in% with parentheses [OK]

Common Mistakes:

• Using wrong operator order
• Typing *%*% instead of %*%
• Using == instead of %in% for membership