Ifelse vectorized function in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use ifelse to assign 'pass' if score is 50 or more, else 'fail'.

R Programming

result <- ifelse(score [1] 50, 'pass', 'fail')

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

A==

B<

C>=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>=' causes wrong results.

Using '==' only checks for exactly 50, not more.

The ifelse function checks if score is greater than or equal to 50 to assign 'pass'.

2fill in blank

medium

Complete the code to assign 'even' if number is divisible by 2, else 'odd'.

R Programming

result <- ifelse(number %% 2 [1] 0, 'even', 'odd')

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

A!=

B<

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' reverses the logic, marking even numbers as odd.

Using '>' or '<' does not correctly check divisibility.

The modulo operator %% returns 0 for even numbers, so we check if it equals 0.

3fill in blank

hard

Fix the error in the ifelse condition to correctly assign 'adult' if age is 18 or more.

R Programming

category <- ifelse(age [1] 18, 'adult', 'minor')

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

A>=

B!=

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' assigns adults incorrectly.

Using '==' only matches exactly 18, missing older ages.

Adults are those with age greater than or equal to 18, so '>=' is correct.

4fill in blank

hard

Fill both blanks to create a vectorized ifelse that labels numbers as 'positive' if greater than zero, else 'non-positive'.

R Programming

labels <- ifelse(numbers [1] 0, 'positive', [2])

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

A>

B'non-positive'

C'negative'

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' in the condition reverses logic.

Using 'negative' instead of 'non-positive' changes meaning.

The condition checks if numbers are greater than zero for 'positive', else assigns 'non-positive'.

5fill in blank

hard

Fill all three blanks to create a vectorized ifelse that labels temperatures as 'hot' if above 30, 'cold' if below 15, else 'warm'.

R Programming

labels <- ifelse(temp [1] 30, 'hot', ifelse(temp [2] 15, 'cold', [3]))

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

A>

B<

C'warm'

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' instead of '>' changes the boundary.

Using wrong labels in the else part.

The first condition checks if temp is greater than 30 for 'hot'. The nested ifelse checks if temp is less than 15 for 'cold'. Otherwise, it assigns 'warm'.

Practice

1. What does the ifelse function in R do?

easy

A. It checks a condition for each element and returns values accordingly.

B. It creates a loop to iterate over elements.

C. It sorts a vector in ascending order.

D. It combines two vectors into one.

Solution

1. Step 1: Understand the purpose of ifelse

   The ifelse function tests a condition for each element in a vector.

2. Step 2: Identify the output behavior

   It returns a new vector with values chosen from the 'yes' or 'no' options based on the condition.

3. Final Answer:

   It checks a condition for each element and returns values accordingly. -> Option A

4. Quick Check:

   ifelse = condition-based selection [OK]

Hint: Think: condition check for each item returns chosen values [OK]

Common Mistakes:

• Confusing ifelse with loops
• Thinking it sorts or merges vectors
• Assuming it modifies original vector in place

2. Which of the following is the correct syntax for using ifelse in R?

easy

A. ifelse(condition, yes, no)

B. ifelse(yes, no, condition)

C. ifelse(condition; yes; no)

D. ifelse(condition -> yes, no)

Solution

1. Step 1: Recall the function signature

   The ifelse function takes three arguments: a condition, a value if true, and a value if false.

2. Step 2: Match the correct order and separators

   The correct syntax uses commas to separate arguments: ifelse(condition, yes, no).

3. Final Answer:

   ifelse(condition, yes, no) -> Option A

4. Quick Check:

   Syntax = ifelse(condition, yes, no) [OK]

Hint: Remember: condition first, then yes, then no, separated by commas [OK]

Common Mistakes:

• Swapping order of arguments
• Using semicolons instead of commas
• Using arrows or other symbols incorrectly

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

nums <- c(5, 10, 15, 20)
result <- ifelse(nums > 10, "big", "small")
print(result)

medium

A. ["big", "big", "small", "small"]

B. ["small", "small", "big", "big"]

C. [5, 10, 15, 20]

D. [TRUE, TRUE, FALSE, FALSE]

Solution

1. Step 1: Evaluate the condition for each element

   Check if each number in nums is greater than 10: 5 > 10 is FALSE, 10 > 10 is FALSE, 15 > 10 is TRUE, 20 > 10 is TRUE.

2. Step 2: Assign values based on condition

   For FALSE, assign "small"; for TRUE, assign "big". So the result vector is ["small", "small", "big", "big"].

3. Final Answer:

   ["small", "small", "big", "big"] -> Option B

4. Quick Check:

   Condition >10 gives small or big [OK]

Hint: Check condition element-wise, assign yes/no values [OK]

Common Mistakes:

• Confusing > with >=
• Returning original numbers instead of labels
• Mixing up true and false outputs

4. Identify the error in this R code snippet:

values <- c(1, 2, 3, 4)
result <- ifelse(values > 2, "high" "low")
print(result)

medium

A. Incorrect vector assignment syntax.

B. Using > operator instead of >=.

C. Using print() instead of cat() to display output.

D. Missing comma between 'high' and 'low' in ifelse arguments.

Solution

1. Step 1: Check the ifelse argument syntax

   The ifelse function requires three arguments separated by commas: condition, yes, no.

2. Step 2: Identify missing comma

   In the code, "high" and "low" are not separated by a comma, causing a syntax error.

3. Final Answer:

   Missing comma between 'high' and 'low' in ifelse arguments. -> Option D

4. Quick Check:

   Arguments must be comma-separated [OK]

Hint: Check commas between all ifelse arguments [OK]

Common Mistakes:

• Omitting commas between arguments
• Confusing operators > and >=
• Thinking print() causes error here

5. You have a numeric vector temps <- c(-5, 0, 10, 20, 30). Use ifelse to create a new vector labels that labels temperatures below 0 as "freezing", between 0 and 20 (inclusive) as "cold", and above 20 as "warm". Which code correctly does this?

hard

A. labels <- ifelse(temps <= 0, "freezing", ifelse(temps < 20, "cold", "warm"))

B. labels <- ifelse(temps < 0, "freezing", ifelse(temps < 20, "cold", "warm"))

C. labels <- ifelse(temps < 0, "freezing", ifelse(temps <= 20, "cold", "warm"))

D. labels <- ifelse(temps < 0, "freezing", ifelse(temps >= 20, "warm", "cold"))

Solution

1. Step 1: Understand the labeling rules

   Label "freezing" if temperature is below 0, "cold" if between 0 and 20 inclusive, and "warm" if above 20.

2. Step 2: Check nested ifelse conditions

   The first ifelse checks temps < 0 for "freezing". The second nested ifelse checks if temps <= 20 for "cold", else "warm".

3. Final Answer:

   labels <- ifelse(temps < 0, "freezing", ifelse(temps <= 20, "cold", "warm")) -> Option C

4. Quick Check:

   Nested ifelse with correct bounds [OK]

Hint: Use nested ifelse for multiple conditions with correct bounds [OK]

Common Mistakes:

• Using < instead of <= for 20 boundary
• Swapping warm and cold labels
• Not nesting ifelse properly