Type checking (class, isa) in MATLAB - Mini Project: Build & Apply

Type Checking with class and isa in MATLAB

📖 Scenario: You are working on a MATLAB program that processes different types of data inputs. To handle them correctly, you need to check the type of each input before processing.

🎯 Goal: Build a MATLAB script that creates variables of different types, sets a type to check against, uses class and isa functions to check types, and prints the results.

📋 What You'll Learn

Create variables of different types: numeric, character array, and cell array

Create a variable called typeToCheck with a string value representing a type

Use class function to get the type of a variable

Use isa function to check if a variable is of a certain type

Print the results of the type checks

💡 Why This Matters

🌍 Real World

Type checking is important when writing programs that handle different kinds of data. It helps avoid errors by making sure the data is the expected type before processing.

💼 Career

Many programming jobs require you to write code that safely handles inputs and data. Knowing how to check types in MATLAB is useful for data analysis, engineering simulations, and scientific computing.

1

Create variables of different types

Create a numeric variable called numVar with value 10, a character array called charVar with value 'hello', and a cell array called cellVar with value {1, 2, 3}.

MATLAB

% Your code here

Hint

Use = to assign values. Numeric values are written as numbers, character arrays in single quotes, and cell arrays in curly braces.

2

Set the type to check

Create a variable called typeToCheck and set it to the string 'double'.

MATLAB

numVar = 10;
charVar = 'hello';
cellVar = {1, 2, 3};
% Your code here

Hint

Use single quotes to create a string in MATLAB.

3

Check types using class and isa

Use the class function to get the type of numVar and store it in numVarType. Then use isa to check if charVar is of type typeToCheck and store the result in isCharVarType.

MATLAB

numVar = 10;
charVar = 'hello';
cellVar = {1, 2, 3};
typeToCheck = 'double';
% Your code here

Hint

Use class(variable) to get the type name as a string. Use isa(variable, typeName) to check if variable is of that type.

4

Print the results

Print the value of numVarType and isCharVarType using disp function.

MATLAB

numVar = 10;
charVar = 'hello';
cellVar = {1, 2, 3};
typeToCheck = 'double';
numVarType = class(numVar);
isCharVarType = isa(charVar, typeToCheck);
% Your code here

Hint

Use disp(variable) to print the value of a variable.

Practice

1. What does the class function in MATLAB return when used on a variable?

easy

A. True if the variable is numeric

B. The exact type name of the variable

C. The size of the variable

D. The value of the variable

Solution

1. Step 1: Understand the purpose of class

   The class function returns the exact type name of the variable, such as 'double', 'char', or a user-defined class. Other choices describe checks for numeric type, size, or value, but class specifically returns the type name as a string.

2. Final Answer:

   The exact type name of the variable -> Option B

3. Quick Check:

   class = exact type name [OK]

Hint: Remember: class gives type name as text [OK]

Common Mistakes:

• Confusing class with isa function
• Thinking class returns size or value
• Assuming class returns a boolean

2. Which of the following is the correct syntax to check if variable x is of class double using isa?

easy

A. class(x) == 'double'

B. isa('double', x)

C. isa(x, 'double')

D. class(x, 'double')

Solution

1. Step 1: Recall isa function syntax

   The correct syntax is isa(variable, 'classname'), so to check if x is a double, use isa(x, 'double'). Using class(x) == 'double' compares strings unreliably, isa('double', x) reverses arguments, and class(x, 'double') has invalid syntax.

2. Final Answer:

   isa(x, 'double') -> Option C

3. Quick Check:

   isa(variable, 'class') syntax [OK]

Hint: isa(variable, 'classname') checks type safely [OK]

Common Mistakes:

• Swapping arguments in isa
• Using == to compare class strings
• Calling class with two arguments

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

x = 5; y = isa(x, 'double'); disp(y);

medium

A. 'double'

B. 0

C. Error

D. 1

Solution

1. Step 1: Trace code execution

   Variable x is assigned 5, which defaults to class double in MATLAB. isa(x, 'double') returns logical true (displayed as 1), and disp(y) outputs 1.

2. Final Answer:

   1 -> Option D

3. Quick Check:

   isa(5, 'double') = 1 [OK]

Hint: Numeric literals are double by default [OK]

Common Mistakes:

• Expecting 0 because 5 looks like int
• Confusing output with class function
• Thinking isa returns string

4. Identify the error in this MATLAB code snippet:

if isa('double', x)
    disp('x is double')
end

medium

A. Arguments of isa are reversed

B. Missing semicolon after disp

C. isa cannot be used inside if

D. No error, code is correct

Solution

1. Step 1: Check isa function argument order

   The correct order is isa(variable, 'classname'), but here arguments are reversed to isa('double', x). A missing semicolon after disp or using isa in if are not errors.

2. Final Answer:

   Arguments of isa are reversed -> Option A

3. Quick Check:

   isa(variable, 'class') order matters [OK]

Hint: Always put variable first in isa() [OK]

Common Mistakes:

• Swapping arguments in isa
• Thinking missing semicolon causes error
• Believing isa can't be used in if

5. You want to write a MATLAB function that accepts either a numeric array or a table. Which code snippet correctly uses isa to check the input type?

hard

A. if isa(input, 'double') || isa(input, 'table')

B. if isa(input, 'array') || isa(input, 'table')

C. if class(input) == 'numeric' || class(input) == 'table'

D. if isa(input, 'numeric') || isa(input, 'table')

Solution

1. Step 1: Identify correct class names and syntax

   In MATLAB, numeric arrays usually have class 'double', not 'numeric' or 'array'. if isa(input, 'double') || isa(input, 'table') correctly checks either using proper isa syntax and logical OR.

2. Final Answer:

   if isa(input, 'double') || isa(input, 'table') -> Option A

3. Quick Check:

   Use isa with correct class names [OK]

Hint: Use isa with exact MATLAB class names [OK]

Common Mistakes:

• Using 'numeric' instead of 'double'
• Using class() with == for strings
• Assuming 'array' is a class name