Cell array creation in MATLAB

Introduction

Cell arrays let you store different types of data together in one container. They are useful when you want to keep numbers, text, or other data mixed in one place.

You want to store a list of names and ages together.

You need to keep different types of data like strings and numbers in one variable.

You want to group results from different calculations that have different data types.

You want to create a flexible container that can hold arrays of different sizes or types.

Syntax

MATLAB

cellArray = {item1, item2, item3, ...};

Use curly braces { } to create a cell array.

Each item inside can be any data type: number, string, array, or even another cell array.

Examples

This creates a cell array with a number, a string, and a numeric array.

MATLAB

myCell = {42, 'hello', [1, 2, 3]};

This creates an empty cell array with no elements.

MATLAB

emptyCell = {};

This creates a cell array with just one element, the number 99.

MATLAB

singleCell = {99};

This creates a cell array where the second element is another cell array.

MATLAB

nestedCell = { 'text', {1, 2, 3} };

Sample Program

This program creates a cell array with a number, a string, and a numeric array. It then prints the whole cell array and each element separately.

MATLAB

clc;
clear;

% Create a cell array with different types of data
mixedCell = {123, 'MATLAB', [10, 20, 30]};

% Display the whole cell array
disp('Original cell array:');
disp(mixedCell);

% Access and display each element separately
for index = 1:length(mixedCell)
    fprintf('Element %d: ', index);
    disp(mixedCell{index});
end

Important Notes

Creating a cell array is fast and uses space proportional to the number of elements.

Access elements with curly braces { } to get the content, or parentheses ( ) to get a sub-cell array.

Common mistake: Using parentheses instead of curly braces to access data inside cells returns a cell, not the data itself.

Use cell arrays when you need to store mixed data types; use regular arrays when all data is the same type.

Summary

Cell arrays hold different types of data together.

Use curly braces { } to create and access cell contents.

They are useful for flexible, mixed-type collections.

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