Switch statement in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple switch statement

What is the output of this R code using switch?

R Programming

result <- switch("b", a = 1, b = 2, c = 3)
print(result)

A NULL

B [1] 2

C [1] 3

D [1] 1

💡 Hint

Remember that switch matches the first argument to the names.

The switch matches the string "b" to the named argument b = 2, so it returns 2.

❓ Predict Output

intermediate

Switch with numeric index

What will this R code print?

R Programming

result <- switch(3, "apple", "banana", "cherry", "date")
print(result)

A [1] "cherry"

B [1] "banana"

C [1] "apple"

D [1] "date"

💡 Hint

When the first argument is a number, switch returns the element at that position.

The number 3 selects the third element, which is "cherry".

🔧 Debug

advanced

Error in switch with unnamed arguments

What error does this R code produce?

R Programming

result <- switch("x", "apple", "banana", "cherry")
print(result)

A [1] "apple"

B Error in switch: EXPR must be a length 1 vector

C NULL

D Error: no matching case found

💡 Hint

If the first argument is a string but no matching name exists, what does switch return?

When the first argument is a string and no matching name is found, switch returns NULL without error.

❓ Predict Output

advanced

Switch with expression and default

What is the output of this R code?

R Programming

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

A [1] 40

B [1] 20

C [1] 30

D [1] 10

💡 Hint

If no named match is found, switch returns the last unnamed argument as default.

Since "z" does not match a, b, or c, switch returns the last unnamed argument 40.

🧠 Conceptual

expert

Behavior of switch with numeric zero

What happens when you run this R code?

R Programming

result <- switch(0, "apple", "banana", "cherry")
print(result)

A [1] "banana"

B [1] "apple"

C [1] "cherry"

D NULL

💡 Hint

Check how switch treats numeric indices outside the valid range.

Numeric indices less than 1 or greater than the number of options cause switch to return NULL.

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