Modifying and adding elements in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to change the second element of the vector to 10.

R Programming

vec <- c(1, 2, 3)
vec[[1]] <- 10
vec

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

A2

B3

C1

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 0 which does not exist in R vectors.

Trying to assign value without specifying index.

The second element of the vector is accessed with index 2, so vec[2] <- 10 changes it to 10.

2fill in blank

medium

Complete the code to add the number 4 at the end of the vector.

R Programming

vec <- c(1, 2, 3)
vec <- c(vec, [1])
vec

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

A5

B4

C3

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the number before the vector which changes the order.

Using incorrect syntax like vec + 4 which does not add elements.

Using c(vec, 4) adds 4 to the end of the vector.

3fill in blank

hard

Fix the error in the code to correctly replace the third element with 7.

R Programming

vec <- c(1, 2, 3)
vec[[1]] <- 7
vec

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

A3

B0

C-1

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 0 which is invalid in R.

Using an index larger than the vector length, which adds a new element instead of replacing the third.

The third element is at index 3, so vec[3] <- 7 correctly replaces it.

4fill in blank

hard

Fill both blanks to create a vector with elements 1, 2, 3, and then add 5 at the end.

R Programming

vec <- c([1], [2], 3)
vec <- c(vec, 5)
vec

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

A1

B2

C4

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong numbers for the first two elements.

Forgetting to add 5 at the end.

The vector starts with 1 and 2, then 3 is added. Then 5 is appended at the end.

5fill in blank

hard

Fill all three blanks to create a vector with elements 10, 20, 30, then replace the second element with 25.

R Programming

vec <- c([1], [2], [3])
vec[2] <- 25
vec

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

A10

B20

C30

D25

Attempts:

3 left

💡 Hint

Common Mistakes

Replacing the wrong element.

Using incorrect numbers in the vector.

The vector is created with 10, 20, 30. Then the second element (20) is replaced with 25.

Practice

1. In R, how do you change the second element of a vector v to 10?

easy

A. v[2] = 10()

B. v(2) = 10

C. v{2} <- 10

D. v[2] <- 10

Solution

1. Step 1: Understand element access in R vectors

   Elements in R vectors are accessed using square brackets [ ] with the position number inside.

2. Step 2: Assign new value to the element

   Use the assignment operator <- to set the new value at the specified position.

3. Final Answer:

   v[2] <- 10 -> Option D

4. Quick Check:

   Use [ ] and <- to modify elements [OK]

Hint: Use square brackets and <- to change elements [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Adding parentheses after the value
• Using curly braces for indexing

2. Which of the following is the correct syntax to add a new element 5 to the end of vector v in R?

easy

A. v + 5

B. v <- c(v, 5)

C. v[+5]

D. v <- v + c(5)

Solution

1. Step 1: Understand how to add elements to a vector

   In R, use the c() function to combine vectors or add elements.

2. Step 2: Combine existing vector with new element

   Use v <- c(v, 5) to add 5 at the end of vector v.

3. Final Answer:

   v <- c(v, 5) -> Option B

4. Quick Check:

   Use c() to add elements [OK]

Hint: Use c() to add elements to vectors [OK]

Common Mistakes:

• Using + operator to add elements
• Incorrect indexing syntax
• Adding vectors without assignment

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

v <- c(1, 2, 3)
v[1] <- 10
v <- c(v, 4)
v

medium

A. [10, 2, 3]

B. [1, 2, 3, 4]

C. [10, 2, 3, 4]

D. [1, 2, 3]

Solution

1. Step 1: Modify first element of vector

   The first line changes the first element from 1 to 10, so vector becomes (10, 2, 3).

2. Step 2: Add new element 4 at the end

   Using c(v, 4) adds 4 to the end, resulting in (10, 2, 3, 4).

3. Final Answer:

   [10, 2, 3, 4] -> Option C

4. Quick Check:

   Modify then add element = [10, 2, 3, 4] [OK]

Hint: Modify first, then add with c() to get final vector [OK]

Common Mistakes:

• Forgetting to assign after adding element
• Not updating the first element correctly
• Confusing vector output format

4. Identify the error in the following R code that tries to add 7 to vector v:

v <- c(1, 2, 3)
v + 7

medium

A. The code adds 7 to each element, not appends 7

B. Using + operator is correct to add elements

C. v + 7 appends 7 correctly to vector

D. Syntax error due to missing assignment operator

Solution

1. Step 1: Understand vector addition vs adding elements

   Using v + 7 adds 7 to each element, but does not append a new element.

2. Step 2: Check for assignment to update vector

   The code does not assign the result back to v, so vector remains unchanged. Also, to add an element, c() should be used.

3. Final Answer:

   The code adds 7 to each element, not appends 7 -> Option A

4. Quick Check:

   Adding elements needs c() and assignment [OK]

Hint: Use c() and <- to add elements, not + alone [OK]

Common Mistakes:

• Using + to append elements
• Not assigning result back to vector
• Confusing element-wise addition with adding elements

5. Given a vector v <- c(2, 4, 6), which code correctly replaces the last element with 8 and then adds 10 at the end?

hard

A. v[length(v)] <- 8; v <- c(v, 10)

B. v[3] = 8; v + 10

C. v[-1] <- 8; v <- c(v, 10)

D. v[length(v)+1] <- 8; v <- c(v, 10)

Solution

1. Step 1: Replace last element using length()

   Use v[length(v)] <- 8 to change the last element (position 3) to 8.

2. Step 2: Add 10 at the end with c()

   Use v <- c(v, 10) to append 10 to the vector.

3. Final Answer:

   v[length(v)] <- 8; v <- c(v, 10) -> Option A

4. Quick Check:

   Use length() to index last element, c() to add [OK]

Hint: Use length(v) to find last element, c() to add new [OK]

Common Mistakes:

• Using negative index incorrectly
• Adding element with + operator
• Assigning to length(v)+1 without c()