Matrix creation in R Programming - Mini Project: Build & Apply

Matrix creation

📖 Scenario: You are working with a small business that tracks sales data in a table format. You want to create a matrix to organize the sales numbers for analysis.

🎯 Goal: Create a matrix in R with specific sales data, set the number of rows, and display the matrix.

📋 What You'll Learn

Create a matrix with exact values

Set the number of rows correctly

Print the matrix to show the data

💡 Why This Matters

🌍 Real World

Matrices are used to organize data in tables, like sales figures, for easy analysis and visualization.

💼 Career

Knowing how to create and manipulate matrices is important for data analysis, statistics, and many programming jobs involving data.

1

Create the sales data matrix

Create a matrix called sales_matrix with these exact values in this order: 10, 20, 30, 40, 50, 60.

R Programming

# Create a matrix called sales_matrix with values 10, 20, 30, 40, 50, 60
# Your code here

Hint

Use the matrix() function with c() to combine the numbers.

2

Set the number of rows

Modify the sales_matrix to have exactly 2 rows by adding the argument nrow = 2 inside the matrix() function.

R Programming

sales_matrix <- matrix(c(10, 20, 30, 40, 50, 60), nrow = 2)
# Your code here

Hint

Add nrow = 2 inside the matrix() function to set rows.

3

Set the number of columns

Modify the sales_matrix to have exactly 3 columns by adding the argument ncol = 3 inside the matrix() function along with nrow = 2.

R Programming

sales_matrix <- matrix(c(10, 20, 30, 40, 50, 60), nrow = 2, ncol = 3)
# Your code here

Hint

Add ncol = 3 along with nrow = 2 inside the matrix() function.

4

Display the matrix

Write a line to print the sales_matrix so you can see the organized sales data.

R Programming

print(sales_matrix)  # Your code here

Hint

Use the print() function with sales_matrix inside.

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