Matrix creation in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a 3x3 matrix filled with numbers 1 to 9.

R Programming

mat <- matrix([1], nrow = 3, ncol = 3)

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

Arep(1, 9)

Bc(1,9)

Cseq(1, 3)

D1:9

Attempts:

3 left

💡 Hint

Common Mistakes

Using c(1,9) creates a vector with only two numbers, not a sequence.

Using seq(1, 3) creates a sequence from 1 to 3, which is too short.

Using rep(1, 9) repeats 1 nine times, not a sequence.

The matrix() function creates a matrix. Using 1:9 fills it with numbers from 1 to 9.

2fill in blank

medium

Complete the code to create a 2x4 matrix filled by rows with numbers 1 to 8.

R Programming

mat <- matrix(1:8, nrow = 2, ncol = 4, [1] = TRUE)

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

Abyrow

Bfill

Crowwise

Dbycol

Attempts:

3 left

💡 Hint

Common Mistakes

Using fill or rowwise which are not valid arguments.

Using bycol which is not a valid argument in matrix().

The argument byrow = TRUE fills the matrix by rows instead of by columns.

3fill in blank

hard

Fix the error in the code to create a 3x3 matrix with numbers 1 to 9.

R Programming

mat <- matrix(1:9, nrow = [1], ncol = 3)

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

A2

B3

C9

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting rows to 2 or 1 which does not fit 9 elements properly.

Setting rows to 9 which creates a 9x3 matrix, too large.

The matrix should have 3 rows and 3 columns to fit numbers 1 to 9 properly.

4fill in blank

hard

Fill both blanks to create a 4x2 matrix filled by columns with numbers 1 to 8.

R Programming

mat <- matrix([1], nrow = [2], ncol = 2)

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

A1:8

B4

C8

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 8 as number of rows which would not match the 2 columns for 8 elements.

Using 2 as number of rows which is too small.

Use 1:8 for the data and 4 for the number of rows to create a 4x2 matrix.

5fill in blank

hard

Fill all three blanks to create a 3x3 matrix filled by rows with numbers 1 to 9.

R Programming

mat <- matrix([1], nrow = [2], ncol = [3], byrow = TRUE)

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

A1:9

B3

D9

Attempts:

3 left

💡 Hint

Common Mistakes

Using 9 for rows or columns which creates a 9x9 matrix.

Not setting byrow = TRUE to fill by rows.

The data is numbers 1 to 9, with 3 rows and 3 columns, filled by rows.

Practice

1. What does the matrix() function in R primarily do?

easy

A. Creates a table of values arranged in rows and columns

B. Generates a list of random numbers

C. Sorts a vector in ascending order

D. Calculates the sum of all elements in a vector

Solution

1. Step 1: Understand the purpose of matrix()

   The matrix() function is designed to create a matrix, which is a table of values arranged in rows and columns.

2. Step 2: Compare with other options

   Options A, B, and C describe different functions or operations unrelated to matrix creation.

3. Final Answer:

   Creates a table of values arranged in rows and columns -> Option A

4. Quick Check:

   matrix() creates tables = D [OK]

Hint: matrix() makes tables with rows and columns [OK]

Common Mistakes:

• Confusing matrix() with functions that generate random numbers
• Thinking matrix() sorts data
• Assuming matrix() sums elements

2. Which of the following is the correct syntax to create a 2x3 matrix filled by rows with numbers 1 to 6 in R?

easy

A. matrix(1:6, nrow=3, ncol=2, byrow=TRUE)

B. matrix(1:6, nrow=2, ncol=3, byrow=TRUE)

C. matrix(1:6, nrow=2, ncol=3, byrow=FALSE)

D. matrix(1:6, nrow=3, ncol=2, byrow=FALSE)

Solution

1. Step 1: Identify matrix dimensions and filling order

   The question asks for a 2 rows by 3 columns matrix filled by rows with numbers 1 to 6.

2. Step 2: Match syntax to requirements

   matrix(1:6, nrow=2, ncol=3, byrow=TRUE) uses nrow=2, ncol=3, and byrow=TRUE, which matches the question exactly.

3. Final Answer:

   matrix(1:6, nrow=2, ncol=3, byrow=TRUE) -> Option B

4. Quick Check:

   2 rows, 3 cols, byrow=TRUE = A [OK]

Hint: Match nrow, ncol, and byrow exactly [OK]

Common Mistakes:

• Swapping nrow and ncol values
• Forgetting to set byrow=TRUE for row-wise filling
• Using byrow=FALSE when row-wise fill is needed

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

m <- matrix(1:6, nrow=2, ncol=3, byrow=FALSE)
print(m)

medium

A. [,1] [,2] [,3]
[1,] 1 4 2
[2,] 3 5 6

B. [[1, 3, 5], [2, 4, 6]]

C. [[1, 2, 3], [4, 5, 6]]

D. [,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6

Solution

1. Step 1: Understand matrix filling by columns

   With byrow=FALSE, the matrix fills column-wise: first column gets 1 and 2, second gets 3 and 4, third gets 5 and 6.

2. Step 2: Write matrix layout

   Row 1: 1, 3, 5
   Row 2: 2, 4, 6

3. Final Answer:

   [,1] [,2] [,3] [1,] 1 3 5 [2,] 2 4 6 -> Option D

4. Quick Check:

   byrow=FALSE fills columns = A [OK]

Hint: byrow=FALSE fills columns top to bottom [OK]

Common Mistakes:

• Assuming byrow=FALSE fills rows instead of columns
• Mixing up row and column indices in output
• Confusing output format with list notation

4. Identify the error in this R code that tries to create a 3x2 matrix:

matrix(1:6, nrow=3, ncol=2, byrow=TRUE, fill=TRUE)

medium

A. The argument 'fill' is not valid in matrix()

B. nrow and ncol values are swapped

C. byrow must be FALSE for this matrix size

D. 1:6 cannot fill a 3x2 matrix

Solution

1. Step 1: Check matrix() arguments

   The matrix() function does not have a fill argument; this causes an error.

2. Step 2: Validate other arguments

   nrow=3 and ncol=2 are valid, byrow=TRUE is allowed, and 1:6 perfectly fills a 3x2 matrix.

3. Final Answer:

   The argument 'fill' is not valid in matrix() -> Option A

4. Quick Check:

   Invalid argument 'fill' causes error = C [OK]

Hint: matrix() has no 'fill' argument [OK]

Common Mistakes:

• Assuming 'fill' is a valid argument
• Swapping nrow and ncol unnecessarily
• Thinking byrow must be FALSE for certain sizes

5. You want to create a 4x4 matrix in R where the numbers 1 to 16 fill the matrix by rows, but every even number should be replaced by 0. Which code correctly achieves this?

hard

A. matrix(ifelse((1:16) %% 2 == 0, 0, 1:16), nrow=4, ncol=4, byrow=FALSE)

B. matrix(ifelse((1:16) %% 2 == 1, 0, 1:16), nrow=4, ncol=4, byrow=TRUE)

C. matrix(ifelse((1:16) %% 2 == 0, 0, 1:16), nrow=4, ncol=4, byrow=TRUE)

D. matrix(ifelse((1:16) %% 2 == 1, 0, 1:16), nrow=4, ncol=4, byrow=FALSE)

Solution

1. Step 1: Replace even numbers with 0

   The expression ifelse((1:16) %% 2 == 0, 0, 1:16) replaces even numbers with 0 and keeps odd numbers as is.

2. Step 2: Create 4x4 matrix filled by rows

   Using nrow=4, ncol=4, and byrow=TRUE fills the matrix row-wise as required.

3. Final Answer:

   matrix(ifelse((1:16) %% 2 == 0, 0, 1:16), nrow=4, ncol=4, byrow=TRUE) -> Option C

4. Quick Check:

   Replace evens with 0, fill by rows = B [OK]

Hint: Use ifelse() and byrow=TRUE for row-wise conditional fill [OK]

Common Mistakes:

• Using byrow=FALSE when row-wise fill is needed
• Replacing odd numbers instead of even
• Not using ifelse() for conditional replacement