Switch statement in R Programming - Mini Project: Build & Apply

Using Switch Statement in R

📖 Scenario: You are creating a simple program to convert a number representing a day of the week into the day's name. This is useful for apps that show schedules or reminders.

🎯 Goal: Build a program that uses the switch() statement in R to print the correct day name for a given day number.

📋 What You'll Learn

Create a variable day_number with a value from 1 to 7

Create a variable default_day with the value "Invalid day"

Use the switch() function with day_number to assign the correct day name to day_name

Print the value of day_name

💡 Why This Matters

🌍 Real World

Switch statements help programs choose actions based on user input or data, like showing the correct day name for a calendar app.

💼 Career

Understanding switch statements is useful for writing clear and efficient code in data analysis, reporting, and software development.

1

Create the day number variable

Create a variable called day_number and set it to 3.

R Programming

# Create a variable called day_number and set it to 3
# Your code here

Hint

Use the assignment operator <- to assign the value 3 to day_number.

2

Create the default day variable

Create a variable called default_day and set it to the string "Invalid day".

R Programming

day_number <- 3
# Create a variable called default_day and set it to "Invalid day"
# Your code here

Hint

Remember to use quotes around the string value.

3

Use switch() to assign the day name

Use the switch() function with day_number to assign the correct day name to a variable called day_name. Use these mappings: 1 = "Monday", 2 = "Tuesday", 3 = "Wednesday", 4 = "Thursday", 5 = "Friday", 6 = "Saturday", 7 = "Sunday". Use default_day as the default value if day_number is not 1 to 7.

R Programming

day_number <- 3
default_day <- "Invalid day"
# Use switch() with day_number to assign day_name
# Your code here

Hint

Convert day_number to a character string inside switch() because switch() matches strings in R.

4

Print the day name

Print the value of the variable day_name.

R Programming

day_number <- 3
default_day <- "Invalid day"
day_name <- switch(as.character(day_number),
                   "1" = "Monday",
                   "2" = "Tuesday",
                   "3" = "Wednesday",
                   "4" = "Thursday",
                   "5" = "Friday",
                   "6" = "Saturday",
                   "7" = "Sunday",
                   default_day)
# Print day_name
# Your code here

Hint

Use the print() function to show the value of day_name.

Practice

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

easy

A. Selects a value from multiple options based on a given expression

B. Repeats a block of code multiple times

C. Defines a new function

D. Creates a loop that runs until a condition is false

Solution

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

   The switch() function evaluates an expression and returns a value based on matching cases.

2. Step 2: Compare with other options

   Options A, C, and D describe loops or function definitions, which are not the role of switch().

3. Final Answer:

   Selects a value from multiple options based on a given expression -> Option A

4. Quick Check:

   Switch chooses one option based on input [OK]

Hint: Switch picks one matching case value quickly [OK]

Common Mistakes:

• Confusing switch with loops like for or while
• Thinking switch defines functions
• Missing the idea of selecting based on expression

2. Which of the following is the correct syntax to use switch() in R?

easy

A. switch(expression, case1 = value1, case2 = value2, default = value3)

B. switch { expression; case1: value1; case2: value2; default: value3 }

C. switch(expression) { case1 => value1; case2 => value2; default => value3 }

D. switch(expression, case1: value1, case2: value2, default: value3)

Solution

1. Step 1: Recall R's switch syntax

   In R, switch() uses named arguments for cases like case1 = value1.

2. Step 2: Check each option

   switch(expression, case1 = value1, case2 = value2, default = value3) matches R syntax. Options A, B, and C use syntax styles from other languages or incorrect separators.

3. Final Answer:

   switch(expression, case1 = value1, case2 = value2, default = value3) -> Option A

4. Quick Check:

   R switch uses named arguments with = [OK]

Hint: Use = for cases inside switch in R [OK]

Common Mistakes:

• Using colon : instead of equals = for cases
• Trying to use curly braces {} with switch
• Confusing R syntax with other languages

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

result <- switch("b", a = 10, b = 20, c = 30, 40)
print(result)

medium

A. 10

B. 20

C. 30

D. 40

Solution

1. Step 1: Identify the switch expression and cases

   The expression is "b". The cases are a=10, b=20, c=30, and a default 40.

2. Step 2: Match the expression to a case

   Since the expression matches case "b", the value 20 is returned.

3. Final Answer:

   20 -> Option B

4. Quick Check:

   Expression "b" matches case b = 20 [OK]

Hint: Match expression string to named case [OK]

Common Mistakes:

• Choosing default value instead of matching case
• Confusing case names with values
• Forgetting switch returns matched case value

4. Identify the error in this R switch statement:

switch(2,
  1 = "one",
  2 = "two",
  3 = "three"
)

medium

A. Switch expression should be a string, not a number

B. Missing a default case

C. Incorrect use of commas between cases

D. Using numeric cases with = instead of unnamed cases

Solution

1. Step 1: Understand switch with numeric expression in R

   When the expression is numeric, switch expects unnamed arguments, not named with =.

2. Step 2: Check the code

   The code uses named cases like 1 = "one", which is invalid syntax for numeric switch.

3. Final Answer:

   Using numeric cases with = instead of unnamed cases -> Option D

4. Quick Check:

   Numeric switch uses unnamed cases, not named with = [OK]

Hint: Use unnamed cases for numeric switch, named for string [OK]

Common Mistakes:

• Using = with numeric cases causes syntax error
• Assuming default case is mandatory
• Thinking switch expression must be string

5. You want to write a switch statement in R that returns "small", "medium", or "large" for numeric input 1, 2, or 3 respectively, and "unknown" for any other number. Which code correctly implements this?

hard

A. switch(as.character(x), '1' = "small", '2' = "medium", '3' = "large", "unknown")

B. switch(x, '1' = "small", '2' = "medium", '3' = "large", "unknown")

C. switch(x, "small", "medium", "large", "unknown")

D. switch(x, 1 = "small", 2 = "medium", 3 = "large", default = "unknown")

Solution

1. Step 1: Understand switch behavior with numeric input

   For numeric input matching positions 1,2,3, use unnamed positional arguments, placing "unknown" as the 4th for other small numbers.

2. Step 2: Analyze each option

   A, C use string literals like '1' = which cause syntax error (unexpected =). D uses numeric literals 1 = which cause syntax error (unexpected =). B uses unnamed arguments, correct for numeric positional matching.

3. Final Answer:

   switch(x, "small", "medium", "large", "unknown") -> Option C

4. Quick Check:

   Numeric switch uses unnamed positional args [OK]

Hint: Unnamed args for numeric switch positions [OK]

Common Mistakes:

• Using numeric cases with = causes syntax error
• Not providing a default value for unmatched cases
• Mixing numeric expression with string case names