Type checking (class, isa) in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if variable x is of class 'double'.

MATLAB

if [1](x, 'double')
    disp('x is a double');
end

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

Aisa

Btype

Cclass

Disclass

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'isa' to check type.

The isa function checks if a variable is of a specified class.

2fill in blank

medium

Complete the code to get the class name of variable y.

MATLAB

typeName = [1](y);

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

Atype

Bclass

Ctypeof

Disa

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'isa' instead of 'class' to get the class name.

The class function returns the class name of a variable as a string.

3fill in blank

hard

Fix the error in the code to check if z is a cell array.

MATLAB

if [1](z, 'cell')
    disp('z is a cell array');
end

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

Aclass

Bisclass

Cisa

Dtype

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'isa' for type checking.

To check if a variable is a cell array, use isa with 'cell'.

4fill in blank

hard

Fill both blanks to create a dictionary of variable names and their classes for variables in the list.

MATLAB

vars = {'a', 'b', 'c'};
classes = containers.Map();
for i = 1:length(vars)
    varName = vars{i};
    classes(varName) = [1](eval([2]));
end

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

Aclass

BvarName

Cisa

Dvars{i}

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'isa' instead of 'class' for getting class name.

Using 'vars{i}' instead of 'varName'.

Use class to get the class name of the variable whose name is stored in varName.

5fill in blank

hard

Fill all three blanks to check if each variable in the list is of class 'double' and store the result in a logical array.

MATLAB

vars = {x, y, z};
isDouble = false(1, length(vars));
for k = 1:length(vars)
    isDouble(k) = [1](vars[2], '[3]');
end

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

Aisa

B{k}

Cdouble

Dclass

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'isa' for checking type.

Using wrong indexing syntax.

Use isa to check if each variable is 'double'. The variable is accessed as vars{k}.

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