Structure arrays in MATLAB - Mini Project: Build & Apply

Structure Arrays

📖 Scenario: You are managing a small library system. Each book has a title, author, and year of publication. You want to organize this information using structure arrays in MATLAB.

🎯 Goal: Create a structure array to store information about books, add a filter condition to find books published after a certain year, and display the filtered list.

📋 What You'll Learn

Create a structure array called library with fields title, author, and year

Add a variable yearThreshold to filter books published after this year

Use logical indexing to create a new structure array recentBooks with books published after yearThreshold

Display the titles and authors of the filtered books

💡 Why This Matters

🌍 Real World

Structure arrays help organize complex data like records of books, employees, or products in a clear way.

💼 Career

Many jobs in data analysis, engineering, and research use structure arrays to manage and process grouped data efficiently.

1

Create the structure array library

Create a structure array called library with these exact entries: title as 'The Alchemist', '1984', 'To Kill a Mockingbird'; author as 'Paulo Coelho', 'George Orwell', 'Harper Lee'; and year as 1988, 1949, 1960 respectively.

MATLAB

# Create the structure array library with the given books
# Your code here

Hint

Use indexing like library(1).title = 'The Alchemist'; to create each book entry.

2

Add the filter variable yearThreshold

Create a variable called yearThreshold and set it to 1970 to filter books published after this year.

MATLAB

library(1).title = 'The Alchemist';
library(1).author = 'Paulo Coelho';
library(1).year = 1988;
library(2).title = '1984';
library(2).author = 'George Orwell';
library(2).year = 1949;
library(3).title = 'To Kill a Mockingbird';
library(3).author = 'Harper Lee';
library(3).year = 1960;
# Create the variable yearThreshold and set it to 1970
# Your code here

Hint

Just write yearThreshold = 1970; on a new line.

3

Filter books published after yearThreshold

Create a new structure array called recentBooks that contains only the books from library where the year field is greater than yearThreshold. Use logical indexing with [library.year].

MATLAB

library(1).title = 'The Alchemist';
library(1).author = 'Paulo Coelho';
library(1).year = 1988;
library(2).title = '1984';
library(2).author = 'George Orwell';
library(2).year = 1949;
library(3).title = 'To Kill a Mockingbird';
library(3).author = 'Harper Lee';
library(3).year = 1960;
yearThreshold = 1970;
# Create recentBooks with books published after yearThreshold
# Your code here

Hint

Use recentBooks = library([library.year] > yearThreshold); to filter.

4

Display the filtered books

Use a for loop with variables i to iterate over recentBooks and print each book's title and author in the format: Title: [title], Author: [author].

MATLAB

library(1).title = 'The Alchemist';
library(1).author = 'Paulo Coelho';
library(1).year = 1988;
library(2).title = '1984';
library(2).author = 'George Orwell';
library(2).year = 1949;
library(3).title = 'To Kill a Mockingbird';
library(3).author = 'Harper Lee';
library(3).year = 1960;
yearThreshold = 1970;
recentBooks = library([library.year] > yearThreshold);
# Use a for loop to print title and author of each recent book
# Your code here

Hint

Use fprintf('Title: %s, Author: %s\n', recentBooks(i).title, recentBooks(i).author); inside a for loop.

Practice

1. What is a structure array in MATLAB used for?

easy

A. To perform matrix multiplication

B. To store only numeric arrays

C. To group related data with different types under named fields

D. To create loops for iteration

Solution

1. Step 1: Understand the purpose of structure arrays

   Structure arrays allow grouping of different types of data under named fields.

2. Step 2: Compare options with the definition

   Only To group related data with different types under named fields correctly describes this use; others describe unrelated concepts.

3. Final Answer:

   To group related data with different types under named fields -> Option C

4. Quick Check:

   Structure arrays = group data by fields [OK]

Hint: Remember: structures group different data types by names [OK]

Common Mistakes:

• Thinking structures only hold numeric data
• Confusing structures with loops or matrices

2. Which of the following is the correct way to create a structure array with fields 'Name' and 'Age' in MATLAB?

easy

A. person = struct('Name', 'Alice', 'Age', 30);

B. person = struct(Name = 'Alice', Age = 30);

C. person = struct['Name', 'Alice', 'Age', 30];

D. person = struct{'Name', 'Alice', 'Age', 30};

Solution

1. Step 1: Recall MATLAB struct syntax

   MATLAB uses struct('field1', value1, 'field2', value2) to create structures.

2. Step 2: Check each option's syntax

   person = struct('Name', 'Alice', 'Age', 30); uses correct parentheses and quotes. Options B, C, D use invalid syntax.

3. Final Answer:

   person = struct('Name', 'Alice', 'Age', 30); -> Option A

4. Quick Check:

   struct uses parentheses and quotes [OK]

Hint: Use parentheses and quotes with struct() [OK]

Common Mistakes:

• Using square or curly brackets instead of parentheses
• Omitting quotes around field names

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

student(1).Name = 'John';
student(1).Score = 85;
student(2).Name = 'Jane';
student(2).Score = 92;
disp(student(2).Name);

medium

A. Jane

B. John

C. 85

D. 92

Solution

1. Step 1: Understand structure array indexing

   student(2) accesses the second element; .Name accesses the 'Name' field.

2. Step 2: Identify the value stored in student(2).Name

   It is 'Jane' as assigned in the code.

3. Final Answer:

   Jane -> Option A

4. Quick Check:

   student(2).Name = 'Jane' [OK]

Hint: Use index and field name to get value [OK]

Common Mistakes:

• Confusing index 1 and 2
• Accessing Score instead of Name

4. Identify the error in this MATLAB code snippet:

car.Make = 'Toyota';
car(1).Model = 'Corolla';
car(1).Year = 2020;

medium

A. Field names must be numeric

B. Missing semicolon after first line

C. Mixing scalar and array structure assignment causes error

D. No error, code runs fine

Solution

1. Step 1: Analyze structure assignment styles

   First line creates scalar structure car with field Make. Next lines assign to car(1), valid for scalar structures.

2. Step 2: Understand MATLAB structure array rules

   MATLAB allows indexing scalar structures and dynamically adding fields; no error occurs.

3. Final Answer:

   No error, code runs fine -> Option D

4. Quick Check:

   Scalar struct indexing + field addition works [OK]

Hint: Scalar structures can be indexed like arrays [OK]

Common Mistakes:

• Thinking scalar and array assignments cannot mix
• Believing field names must be numeric
• Assuming missing semicolons cause errors

5. Given a structure array books with fields Title and Pages, how do you create a new structure array shortBooks containing only books with less than 100 pages?

hard

A. shortBooks = books(books.Pages < 100);

B. shortBooks = books([books.Pages] < 100);

C. shortBooks = books{books.Pages < 100};

D. shortBooks = books(books.Pages > 100);

Solution

1. Step 1: Extract numeric array of Pages

   Use [books.Pages] to get all Pages values as a numeric array.

2. Step 2: Use logical indexing to filter

   Compare with < 100 to get logical indices, then index books with these.

3. Step 3: Check syntax correctness

   shortBooks = books([books.Pages] < 100); correctly uses parentheses and logical indexing; others are incorrect.

4. Final Answer:

   shortBooks = books([books.Pages] < 100); -> Option B

5. Quick Check:

   Logical indexing with [books.Pages] works [OK]

Hint: Use [struct.field] for numeric indexing [OK]

Common Mistakes:

• Using curly braces {} instead of parentheses ()
• Forgetting to use brackets [] around field extraction
• Using wrong comparison operator