For loop in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a for loop.

R Programming

for (i in [1]) {
  print(i)
}

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

Ac(1,5)

B1:5

Cseq(5,1)

Drange(1,5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using c(1,5) which creates a vector with only two elements: 1 and 5.

Using seq(5,1) which counts backwards from 5 to 1.

Using range(1,5) which is not a valid function in R.

The expression 1:5 creates a sequence from 1 to 5 in R, which the for loop iterates over.

2fill in blank

medium

Complete the code to calculate the sum of numbers from 1 to 10 using a for loop.

R Programming

total <- 0
for (num in 1:10) {
  total <- total + [1]
}
print(total)

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

Anum

Btotal

C1:10

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the whole sequence 1:10 instead of the current number.

Adding the total to itself causing incorrect results.

Using sum which is a function, not a variable.

Inside the loop, we add the current number num to the total sum.

3fill in blank

hard

Fix the error in the for loop that prints each letter in the vector letters.

R Programming

letters <- c('a', 'b', 'c')
for ([1] in letters) {
  print(letter)
}

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

Ai

Bletters

Cletter

Dl

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name in the loop header and inside the loop.

Using the whole vector as the loop variable.

Using a variable name not defined in the loop.

The loop variable should be letter to match the variable used inside the loop.

4fill in blank

hard

Fill both blanks to create a named vector with squares of numbers greater than 3.

R Programming

nums <- 1:5
squares <- c()
for ([1] in nums) {
  if ([2] > 3) {
    squares[as.character(num)] <- num^2
  }
}

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

Anum

Bi

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for both blanks causing confusion.

Using undefined variables in the condition.

Not matching variable names inside the loop.

The loop variable is i, and the condition checks if num is greater than 3.

5fill in blank

hard

Fill all three blanks to create a list of even numbers and their squares from 1 to 6.

R Programming

evens <- list()
for ([1] in 1:6) {
  if ([2] %% 2 == 0) {
    evens[[as.character([3])]] <- [2]^2
  }
}

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

Anum

Bi

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing variable names causing undefined variable errors.

Using different variables in the condition and list key.

Not using the loop variable consistently.

The loop variable is i, used consistently in the condition and as the list key.

Practice

1. What does a for loop do in R programming?

easy

A. Stops the program immediately

B. Creates a new variable

C. Defines a new function

D. Repeats a block of code for each item in a sequence

Solution

1. Step 1: Understand the purpose of a for loop

   A for loop is used to repeat actions multiple times, once for each item in a sequence.

2. Step 2: Match the description to the options

   Repeats a block of code for each item in a sequence correctly describes this behavior, while others describe unrelated actions.

3. Final Answer:

   Repeats a block of code for each item in a sequence -> Option D

4. Quick Check:

   For loop = repeat for each item [OK]

Hint: For loops repeat code for each item in a list or sequence [OK]

Common Mistakes:

• Confusing for loop with function definition
• Thinking for loop stops the program
• Believing for loop creates variables only

2. Which of the following is the correct syntax for a for loop in R?

easy

A. for (i; i < 5; i++) { print(i) }

B. for (i in 1:5) { print(i) }

C. for i = 1 to 5 { print(i) }

D. loop (i in 1 to 5) { print(i) }

Solution

1. Step 1: Recall R for loop syntax

   In R, the for loop uses the format: for (variable in sequence) { code }

2. Step 2: Compare options to correct syntax

   for (i in 1:5) { print(i) } matches the correct syntax. Options A, B, and D use syntax from other languages or incorrect forms.

3. Final Answer:

   for (i in 1:5) { print(i) } -> Option B

4. Quick Check:

   R for loop = for (var in sequence) [OK]

Hint: Use 'for (var in sequence)' syntax in R [OK]

Common Mistakes:

• Using 'for i = 1 to 5' like other languages
• Using C-style for loop syntax
• Writing 'loop' instead of 'for'

3. What will be the output of this R code?

for (i in 1:3) {
  print(i * 2)
}

medium

A. [1] 2 [1] 4 [1] 6

B. [1] 1 [1] 2 [1] 3

C. [1] 3 [1] 6 [1] 9

D. Error: object 'i' not found

Solution

1. Step 1: Understand the loop iterations

   The loop runs with i = 1, 2, 3.

2. Step 2: Calculate print output for each i

   For i=1: print(2), i=2: print(4), i=3: print(6).

3. Final Answer:

   [1] 2 [1] 4 [1] 6 -> Option A

4. Quick Check:

   Multiply i by 2 each loop [OK]

Hint: Multiply loop variable by 2 inside print [OK]

Common Mistakes:

• Printing i instead of i*2
• Confusing output format
• Expecting a single combined print

4. Identify the error in this R for loop:

for i in 1:4 {
  print(i)
}

medium

A. Loop variable should be a string

B. Using curly braces instead of parentheses

C. Missing parentheses around the loop variable and sequence

D. Incorrect print function usage

Solution

1. Step 1: Check for correct for loop syntax in R

   R requires parentheses around the loop variable and sequence: for (i in 1:4) { ... }

2. Step 2: Identify the error in given code

   The code misses parentheses around 'i in 1:4', causing a syntax error.

3. Final Answer:

   Missing parentheses around the loop variable and sequence -> Option C

4. Quick Check:

   For loop needs parentheses ( ) [OK]

Hint: Always put parentheses after 'for' in R [OK]

Common Mistakes:

• Omitting parentheses around 'i in 1:4'
• Confusing braces and parentheses
• Thinking print syntax is wrong

5. You want to create a vector of squares of numbers 1 to 5 using a for loop in R. Which code correctly does this?

hard

A. squares <- c()
for (i in 1:5) {
squares[i] <- i^2
}
squares

B. for (i in 1:5) {
squares <- i^2
}
squares

C. squares <- 1:5
for (i in squares) {
squares[i] = i * 2
}
squares

D. squares <- c()
for i in 1:5 {
squares[i] <- i^2
}
squares

Solution

1. Step 1: Initialize an empty vector to store results

   squares <- c() for (i in 1:5) { squares[i] <- i^2 } squares initializes 'squares' as an empty vector to store squares.

2. Step 2: Use a for loop to assign squares to each position

   Inside the loop, squares[i] <- i^2 correctly stores the square of i at position i.

3. Step 3: Check other options for errors

   for (i in 1:5) { squares <- i^2 } squares overwrites 'squares' each time, losing previous values. squares <- 1:5 for (i in squares) { squares[i] = i * 2 } squares multiplies by 2, not square. squares <- c() for i in 1:5 { squares[i] <- i^2 } squares misses parentheses in for loop syntax.

4. Final Answer:

   squares <- c() for (i in 1:5) { squares[i] <- i^2 } squares -> Option A

5. Quick Check:

   Initialize vector, assign squares in loop [OK]

Hint: Initialize vector before loop, assign squares by index [OK]

Common Mistakes:

• Not initializing vector before loop
• Overwriting vector inside loop
• Wrong loop syntax without parentheses