Operator precedence in R Programming - Mini Project: Build & Apply

Operator precedence

📖 Scenario: Imagine you are calculating the total cost of items in a shopping cart with discounts and taxes. You need to understand how R calculates expressions with different operators.

🎯 Goal: Learn how operator precedence affects the result of arithmetic expressions in R by creating variables and calculating values step-by-step.

📋 What You'll Learn

Create variables with exact numeric values

Use arithmetic operators with correct precedence

Use parentheses to change precedence

Print the final calculated result

💡 Why This Matters

🌍 Real World

Calculating prices with discounts and taxes is common in shopping and billing systems.

💼 Career

Understanding operator precedence helps avoid bugs in financial calculations and data analysis.

1

Create initial price variables

Create three variables called price1, price2, and price3 with values 100, 50, and 25 respectively.

R Programming

# Create variables price1, price2, and price3 with values 100, 50, and 25
# Your code here

Hint

Use the assignment operator <- to assign values to variables.

2

Create discount and tax rate variables

Create two variables called discount and tax_rate with values 0.1 and 0.05 respectively.

R Programming

price1 <- 100
price2 <- 50
price3 <- 25
# Create variables discount and tax_rate with values 0.1 and 0.05
# Your code here

Hint

Remember to use <- to assign values.

3

Calculate total price with operator precedence

Create a variable called total_price that calculates the sum of price1, price2, and price3, then applies the discount, and finally adds tax. Use the expression: (price1 + price2 + price3) * (1 - discount) * (1 + tax_rate).

R Programming

price1 <- 100
price2 <- 50
price3 <- 25
discount <- 0.1
tax_rate <- 0.05
# Calculate total_price using operator precedence
# Your code here

Hint

Use parentheses to control the order of operations.

4

Print the total price

Write a print() statement to display the value of total_price.

R Programming

price1 <- 100
price2 <- 50
price3 <- 25
discount <- 0.1
tax_rate <- 0.05
total_price <- (price1 + price2 + price3) * (1 - discount) * (1 + tax_rate)
# Print the total_price
# Your code here

Hint

Use print(total_price) to show the result.

Practice

1. In R, which operator has the highest precedence among these: +, *, ^, -?

easy

A. Subtraction (-)

B. Multiplication (*)

C. Addition (+)

D. Exponentiation (^)

Solution

1. Step 1: Recall operator precedence rules in R

   Exponentiation (^) has higher precedence than multiplication, addition, and subtraction.

2. Step 2: Compare given operators

   Among +, *, ^, and -, ^ is evaluated first.

3. Final Answer:

   Exponentiation (^) -> Option D

4. Quick Check:

   ^ > * > +, - [OK]

Hint: Remember: powers before multiply, multiply before add [OK]

Common Mistakes:

• Thinking multiplication is higher than exponentiation
• Confusing addition and subtraction precedence
• Ignoring operator precedence order

2. Which of the following R expressions is syntactically correct and respects operator precedence?

easy

A. 3 + 4 ** 2

B. 3 + 4 * 2

C. 3 + (4 * ) 2

D. 3 + * 4 2

Solution

1. Step 1: Check each expression for syntax correctness

   3 + 4 * 2 is a valid expression: addition and multiplication with correct syntax. Options A, B, and C have syntax errors.

2. Step 2: Confirm operator precedence in 3 + 4 * 2

   Multiplication happens before addition, so 4 * 2 is evaluated first, then added to 3.

3. Final Answer:

   3 + 4 * 2 -> Option B

4. Quick Check:

   Valid syntax and precedence respected [OK]

Hint: Check for valid operator placement and parentheses [OK]

Common Mistakes:

• Using invalid operators like ** in R
• Misplacing operators causing syntax errors
• Incorrect parentheses usage

3. What is the output of this R code?

result <- 2 + 3 * 4 ^ 2
print(result)

medium

A. 50

B. 74

C. 200

D. 100

Solution

1. Step 1: Evaluate exponentiation first

   4 ^ 2 equals 16.

2. Step 2: Multiply then add

   Multiply 3 by 16 to get 48, then add 2: 2 + 48 = 50.

3. Step 3: Confirm the calculation

   2 + 3 * 4 ^ 2 = 2 + 3 * 16 = 2 + 48 = 50.

4. Final Answer:

   50 -> Option A

5. Quick Check:

   ^ then * then + = 50 [OK]

Hint: Calculate powers first, then multiply, then add [OK]

Common Mistakes:

• Adding before multiplying
• Ignoring exponentiation precedence
• Misreading the expression order

4. Identify the error in this R expression:

value <- 5 + 2 * (3 - 1

medium

A. Missing closing parenthesis

B. Incorrect operator usage

C. Multiplication should be addition

D. No error, expression is correct

Solution

1. Step 1: Check parentheses balance

   The expression has an opening parenthesis after 2 * but no closing parenthesis.

2. Step 2: Confirm syntax error due to missing parenthesis

   R requires matching parentheses; missing one causes syntax error.

3. Final Answer:

   Missing closing parenthesis -> Option A

4. Quick Check:

   Parentheses must be balanced [OK]

Hint: Count opening and closing parentheses carefully [OK]

Common Mistakes:

• Ignoring missing parentheses
• Assuming operators are wrong instead
• Not checking syntax errors first

5. Given the vector v <- c(1, 2, 3), what is the result of this expression in R?

result <- 10 / 2 * v + 1

Choose the correct output.

hard

A. [1] 6 7 8

B. [1] 11 12 13

C. [1] 6 11 16

D. [1] 5 10 15

Solution

1. Step 1: Evaluate division and multiplication first

   10 / 2 equals 5, then multiply by vector v: 5 * c(1,2,3) = c(5,10,15).

2. Step 2: Add 1 to each element

   Add 1 to each element: c(5,10,15) + 1 = c(6,11,16).

3. Final Answer:

   [1] 6 11 16 -> Option C

4. Quick Check:

   Division and multiplication before addition [OK]

Hint: Do division and multiplication before addition on vectors [OK]

Common Mistakes:

• Adding 1 before multiplication
• Ignoring vectorized operations
• Misordering division and multiplication