Cell array creation in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this cell array creation code?

Consider the following MATLAB code that creates a cell array. What will be the content of C after running it?

MATLAB

C = {1, 'text', [2 3 4]; true, {5,6}, pi};
disp(C);

A A 2x3 cell array where C{1,1} is the string '1' and C{2,2} is the number 6

B A 3x2 cell array with numbers and strings mixed incorrectly causing an error

C A numeric matrix with elements 1, 'text', [2 3 4], true, {5,6}, pi

D A 2x3 cell array where C{1,2} is the string 'text' and C{2,3} is the number pi

💡 Hint

Remember that curly braces {} create cell arrays and each element can hold different types.

The code creates a 2-by-3 cell array. Each cell can hold different data types. For example, C{1,2} holds the string 'text', and C{2,3} holds the value of pi.

❓ Predict Output

intermediate

What is the size of the cell array created here?

What is the size of the cell array C after executing this code?

C = cell(3,2);

MATLAB

C = cell(3,2);
sizeC = size(C);

A [3 2]

B [2 3]

C [1 6]

D [6 1]

💡 Hint

The cell function creates a cell array with the given number of rows and columns.

The cell(3,2) command creates a cell array with 3 rows and 2 columns, so its size is [3 2].

🔧 Debug

advanced

Identify the error in this cell array creation

This code is intended to create a 1x3 cell array with different types of elements. What error will MATLAB show when running it?

C = {1, 2, 3; 4, 5};

MATLAB

C = {1, 2, 3; 4, 5};

A Error: Dimensions of arrays being concatenated are not consistent.

B No error, creates a 2x3 cell array with missing elements filled with empty cells.

C Error: Cell arrays cannot contain numeric values.

D Error: Missing semicolon at the end of the line.

💡 Hint

Check the number of elements in each row when creating a cell array with multiple rows.

The first row has 3 elements, but the second row has only 2. MATLAB requires all rows to have the same number of elements when creating arrays, so it throws a dimension mismatch error.

🧠 Conceptual

advanced

Which option correctly creates a nested cell array?

You want to create a cell array C where the second element is itself a cell array containing numbers 10 and 20. Which code does this correctly?

A C = {5; {10, 20}; 'hello'};

B C = {5, [10, 20], 'hello'};

C C = {5, {10, 20}, 'hello'};

D C = {5, {10; 20}, 'hello'};

💡 Hint

Use curly braces inside the cell array to create nested cells.

Option C creates a 1x3 cell array where the second element is a 1x2 cell array containing 10 and 20. Option C uses a numeric array, not a cell. Option C creates a 3x1 cell array (column), not 1x3. Option C creates a nested cell with a column cell array inside, which is valid but changes the shape.

❓ Predict Output

expert

What is the output of this complex cell array indexing?

Given the cell array C = {1, {2, 3}, 4};, what is the output of disp(C{2}{1})?

MATLAB

C = {1, {2, 3}, 4};
disp(C{2}{1});

A 3

B 2

C {2, 3}

D Error: Cell contents reference from a non-cell array object.

💡 Hint

Remember that C{2} accesses the second cell content, which is itself a cell array, then {1} accesses its first element.

C{2} is the cell array {2, 3}. Then C{2}{1} accesses the first element inside that nested cell, which is the number 2.

Practice

1. What is the correct way to create a cell array in MATLAB that contains a number, a string, and a logical value?

easy

A. myCell = [42, 'hello', true];

B. myCell = (42, 'hello', true);

C. myCell = {42, 'hello', true};

D. myCell = <42, 'hello', true>;

Solution

1. Step 1: Understand cell array syntax

   Cell arrays use curly braces { } to hold mixed data types.

2. Step 2: Identify correct syntax for mixed types

   myCell = {42, 'hello', true}; uses curly braces with different types: number, string, logical.

3. Final Answer:

   myCell = {42, 'hello', true}; -> Option C

4. Quick Check:

   Curly braces create cell arrays [OK]

Hint: Use curly braces { } for cell arrays, not square brackets [ ] [OK]

Common Mistakes:

• Using square brackets instead of curly braces
• Using parentheses instead of curly braces
• Using angle brackets which are invalid

2. Which of the following is the correct syntax to create a 2x2 cell array with elements 1, 'a', 3.14, and false?

easy

A. C = [1, 'a'; 3.14, false];

B. C = {1, 'a'; 3.14, false};

C. C = {1; 'a'; 3.14; false};

D. C = (1, 'a'; 3.14, false);

Solution

1. Step 1: Recall cell array 2D syntax

   Use curly braces { } with semicolons for rows and commas for columns.

2. Step 2: Check each option

   C = {1, 'a'; 3.14, false}; correctly uses { } with two rows and two columns separated by ; and ,.

3. Final Answer:

   C = {1, 'a'; 3.14, false}; -> Option B

4. Quick Check:

   Curly braces + semicolon for rows = correct 2D cell array [OK]

Hint: Use semicolon to separate rows inside curly braces [OK]

Common Mistakes:

• Using square brackets which create numeric arrays
• Using commas instead of semicolons for rows
• Using parentheses which are invalid for arrays

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

myCell = {10, 'MATLAB'; 'false', 3.5};
disp(myCell{2,1});

medium

A. false

B. 3.5

C. 'MATLAB'

D. 10

Solution

1. Step 1: Understand cell content access

   Using curly braces with indices accesses the content inside the cell.

2. Step 2: Identify the element at row 2, column 1

   myCell{2,1} is the element in second row, first column, which is 'false' as a string.

3. Final Answer:

   'false' -> Option A

4. Quick Check:

   myCell{2,1} = 'false' [OK]

Hint: Use curly braces { } to get cell content, not parentheses ( ) [OK]

Common Mistakes:

• Using parentheses instead of curly braces to access content
• Confusing row and column indices
• Expecting the whole cell instead of content

4. Consider this MATLAB code snippet:

C = {1, 2, 3; 4, 5, 6};
val = C(2,3);

What is the issue with this code if you want to get the number 6 as a value?

medium

A. C(2,3) returns a cell, not the content inside the cell

B. C(2,3) is invalid syntax for cell arrays

C. C(2,3) returns the number 6 directly

D. C(2,3) returns an error because of wrong indexing

Solution

1. Step 1: Understand difference between () and {}

   Parentheses () return a cell array subset, curly braces {} return content.

2. Step 2: Analyze C(2,3)

   C(2,3) returns a 1x1 cell containing 6, not the number 6 itself.

3. Final Answer:

   C(2,3) returns a cell, not the content inside the cell -> Option A

4. Quick Check:

   Use curly braces to get content: C{2,3} [OK]

Hint: Use curly braces { } to get cell content, parentheses () return cells [OK]

Common Mistakes:

• Using parentheses expecting content instead of cell
• Confusing cell array indexing with numeric array indexing
• Expecting direct numeric output from parentheses indexing

5. You want to create a cell array that stores a numeric vector, a string, and another cell array inside it. Which of the following correctly creates such a nested cell array?

hard

A. nestedCell = {[1, 2, 3], 'text', [true; false]};

B. nestedCell = {[1, 2, 3], 'text', [true, false]};

C. nestedCell = {[1, 2, 3], 'text', (true, false)};

D. nestedCell = {[1, 2, 3], 'text', {true, false}};

Solution

1. Step 1: Identify nested cell array syntax

   To nest a cell array inside another, use curly braces { } inside the main cell array.

2. Step 2: Check each option for correct nesting

   nestedCell = {[1, 2, 3], 'text', {true, false}}; uses {true, false} as a nested cell array inside the main cell array.

3. Final Answer:

   nestedCell = {[1, 2, 3], 'text', {true, false}}; -> Option D

4. Quick Check:

   Curly braces inside curly braces create nested cells [OK]

Hint: Use curly braces inside curly braces for nested cell arrays [OK]

Common Mistakes:

• Using square brackets for nested cell arrays
• Using parentheses which are invalid
• Using semicolons inside nested cell arrays incorrectly