Vector recycling behavior in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a vector that repeats the elements of c(1, 2) to length 6.

R Programming

rep(c(1, 2), [1] = 3)

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

Atimes

Beach

Clength.out

Drepeat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'each' repeats each element individually, not the whole vector.

Using 'length.out' tries to set the total length, not the repeat count.

The times argument tells rep() how many times to repeat the whole vector.

2fill in blank

medium

Complete the code to add two vectors with different lengths using recycling.

R Programming

c(1, 2, 3, 4) + c(10, [1])

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

A20, 30, 40, 50

B20

C20, 30

D20, 30, 40

Attempts:

3 left

💡 Hint

Common Mistakes

Using a vector with length 1 does not show recycling clearly.

Using a vector longer than the first causes an error.

The shorter vector c(10, 20, 30) is recycled to match the length of the longer vector c(1, 2, 3, 4). Here, only 10, 20 are needed to fill the blank to make recycling happen.

3fill in blank

hard

Fix the error in the code that tries to add vectors of incompatible lengths.

R Programming

c(1, 2, 3) + c(10, 20, 30, [1])

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

A50

B40

C60

D70

Attempts:

3 left

💡 Hint

Common Mistakes

Adding vectors of lengths that are not multiples causes warnings.

Adding vectors of different lengths without recycling causes errors.

The second vector has length 4, which is not a multiple of 3, so recycling causes a warning. Removing the last element fixes the error.

4fill in blank

hard

Fill both blanks to create a vector that recycles elements of c(1, 2) to length 5 and then multiply by 2.

R Programming

rep(c(1, 2), [1] = 5) * [2]

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

Alength.out

Btimes

C2

Deach

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'times' instead of 'length.out' changes repetition count, not length.

Multiplying by a vector instead of a number causes unexpected results.

length.out = 5 makes the vector length 5 by recycling, and multiplying by 2 doubles each element.

5fill in blank

hard

Fill all three blanks to create a named vector with lengths of words longer than 3 letters.

R Programming

lengths = { [1]: [2] for word in words if nchar(word) [3] 3 }

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

Aword

Bnchar(word)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' filters the wrong words.

Swapping names and values causes incorrect vector structure.

This creates a named vector where names are words and values are their lengths, but only for words longer than 3 letters.

Practice

1. What happens in R when you add two vectors of different lengths, like c(1, 2, 3) + c(4, 5)?

easy

A. R throws an error because vector lengths differ.

B. Only the first two elements are added, and the rest are ignored.

C. The shorter vector is repeated to match the longer vector's length before addition.

D. The result is a vector of length 2 with NA values.

Solution

1. Step 1: Understand vector lengths

   The first vector has length 3, the second has length 2.

2. Step 2: Apply recycling rule

   The shorter vector c(4, 5) is repeated to become c(4, 5, 4) to match length 3.

3. Final Answer:

   The shorter vector is repeated to match the longer vector's length before addition. -> Option C

4. Quick Check:

   Vector recycling repeats shorter vector [OK]

Hint: Short vector repeats to match longer vector length [OK]

Common Mistakes:

• Thinking R throws an error for different lengths
• Assuming vectors must be same length without recycling
• Ignoring recycling and expecting NA values

2. Which of the following is the correct syntax to add two vectors a and b in R, using vector recycling?

easy

A. a + b

B. add(a, b)

C. a & b

D. sum(a, b)

Solution

1. Step 1: Identify vector addition syntax in R

   In R, adding vectors element-wise is done with the + operator.

2. Step 2: Check other options

   add() is not a base R function; & is logical AND; sum() sums all elements, not element-wise.

3. Final Answer:

   a + b -> Option A

4. Quick Check:

   Use + for element-wise vector addition [OK]

Hint: Use + operator for vector addition in R [OK]

Common Mistakes:

• Using sum() which sums all elements, not element-wise
• Using & which is logical AND, not addition
• Assuming add() is a base R function

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

v1 <- c(10, 20, 30, 40)
v2 <- c(1, 2)
v1 + v2

medium

A. [11, 22, 33, 44]

B. [11, 22, 31, 42]

C. [11, 22, 31, 41]

D. Error due to length mismatch

Solution

1. Step 1: Check vector lengths

   v1 has length 4, v2 has length 2.

2. Step 2: Apply recycling

   v2 repeats as c(1, 2, 1, 2). Adding element-wise:
   10+1=11, 20+2=22, 30+1=31, 40+2=42.

3. Final Answer:

   [11, 22, 31, 42] -> Option B

4. Quick Check:

   Recycle shorter vector and add element-wise [OK]

Hint: Repeat shorter vector to match length, then add [OK]

Common Mistakes:

• Adding only first two elements and ignoring recycling
• Expecting error due to different lengths
• Misaligning recycled elements

4. Consider this R code:

x <- c(5, 10, 15)
y <- c(2, 4, 6, 8)
z <- x + y

What is the problem and how to fix it?

medium

A. Lengths differ and 3 does not divide 4; fix by making lengths compatible.

B. No problem; code runs fine with recycling.

C. Syntax error due to missing parentheses; add parentheses.

D. Vectors must be same length; truncate longer vector.

Solution

1. Step 1: Check vector lengths

   x length is 3, y length is 4.

2. Step 2: Understand recycling warning

   3 does not divide 4 evenly, so R will recycle x but give a warning about length mismatch.

3. Step 3: Fix the problem

   Make vector lengths compatible, e.g., use length 6 or 12, or truncate longer vector.

4. Final Answer:

   Lengths differ and 3 does not divide 4; fix by making lengths compatible. -> Option A

5. Quick Check:

   Unequal lengths without exact multiple cause warnings [OK]

Hint: Lengths must be multiples to avoid warnings [OK]

Common Mistakes:

• Ignoring recycling warning
• Assuming code runs without warnings
• Trying to fix with syntax changes

5. You have two vectors:

v1 <- c(3, 6, 9, 12, 15)
v2 <- c(1, 2)

You want to multiply them element-wise without warnings and get a vector of length 7 by repeating both vectors appropriately. Which code achieves this?

hard

A. rep(v1, each=2) * rep(v2, times=5)

B. v1 * v2

C. v1 + v2

D. rep(v1, length.out=7) * rep(v2, length.out=7)

Solution

1. Step 1: Understand desired output length

   You want a length 7 vector, so both vectors must be length 7.

2. Step 2: Use rep() with length.out

   Using rep(v1, length.out=7) repeats v1 to length 7; similarly for v2.

3. Step 3: Multiply element-wise

   Multiplying these repeated vectors gives length 7 without warnings.

4. Final Answer:

   rep(v1, length.out=7) * rep(v2, length.out=7) -> Option D

5. Quick Check:

   Repeat vectors to same length before operation [OK]

Hint: Use rep() with length.out to match lengths [OK]

Common Mistakes:

• Using direct multiplication causing warnings
• Using rep() with each or times incorrectly
• Adding vectors instead of multiplying