Special operators (%in%, %*%) in R Programming - Mini Project: Build & Apply

Using Special Operators %in% and %*% in R

📖 Scenario: You are working with a small store's inventory and sales data. You want to check which products sold are in the inventory and calculate total sales using matrix multiplication.

🎯 Goal: Build a simple R script that uses the %in% operator to check product membership and the %*% operator to multiply sales quantities by prices.

📋 What You'll Learn

Create a character vector called inventory with product names: "apple", "banana", "orange"

Create a character vector called sold with product names: "banana", "kiwi"

Create a numeric matrix called sales_qty with values c(10, 5) as a 1-row matrix

Create a numeric matrix called prices with values c(2, 3) as a 2-row, 1-column matrix

Use %in% to check which sold products are in inventory

Use %*% to multiply sales_qty by prices to get total sales

Print the logical vector result of membership check

Print the total sales value

💡 Why This Matters

🌍 Real World

Checking product availability and calculating sales totals are common tasks in retail and inventory management.

💼 Career

Understanding these operators helps in data analysis roles, especially when working with product data and sales reports.

1

Create product vectors

Create a character vector called inventory with these exact products: "apple", "banana", "orange". Also create a character vector called sold with these exact products: "banana", "kiwi".

R Programming

# Create the inventory vector with 'apple', 'banana', 'orange'
# Create the sold vector with 'banana', 'kiwi'
# Your code here

Hint

Use the c() function to create vectors with exact product names.

2

Create sales quantity and price matrices

Create a numeric matrix called sales_qty with values c(10, 5) arranged as 1 row and 2 columns. Create a numeric matrix called prices with values c(2, 3) arranged as 2 rows and 1 column.

R Programming

inventory <- c("apple", "banana", "orange")
sold <- c("banana", "kiwi")
# Create sales_qty as 1x2 matrix with values 10 and 5
# Create prices as 2x1 matrix with values 2 and 3
# Your code here

Hint

Use the matrix() function with nrow and ncol to create matrices.

3

Check sold products in inventory and calculate total sales

Use the %in% operator to create a logical vector called in_inventory that checks which products in sold are also in inventory. Use the %*% operator to multiply sales_qty by prices and store the result in total_sales.

R Programming

inventory <- c("apple", "banana", "orange")
sold <- c("banana", "kiwi")
sales_qty <- matrix(c(10, 5), nrow = 1, ncol = 2)
prices <- matrix(c(2, 3), nrow = 2, ncol = 1)
# Use %in% to check which sold products are in inventory and save to in_inventory
# Use %*% to multiply sales_qty by prices and save to total_sales
# Your code here

Hint

Use %in% between sold and inventory. Use %*% between sales_qty and prices.

4

Print the results

Print the logical vector in_inventory to show which sold products are in inventory. Then print the numeric value total_sales to show total sales amount.

R Programming

inventory <- c("apple", "banana", "orange")
sold <- c("banana", "kiwi")
sales_qty <- matrix(c(10, 5), nrow = 1, ncol = 2)
prices <- matrix(c(2, 3), nrow = 2, ncol = 1)
in_inventory <- sold %in% inventory
total_sales <- sales_qty %*% prices
# Print in_inventory
# Print total_sales
# Your code here

Hint

Use print() to show the values of in_inventory and total_sales.

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