Type conversion functions in MATLAB - Mini Project: Build & Apply

Type Conversion Functions in MATLAB

📖 Scenario: You are working with sensor data that comes as text strings. To analyze the data, you need to convert these text strings into numbers.

🎯 Goal: Learn how to convert text strings to numbers and numbers to text strings using MATLAB's type conversion functions.

📋 What You'll Learn

Create a cell array of text strings representing numbers

Create a variable to hold the number of elements

Convert the cell array of strings to a numeric array

Convert the numeric array back to a cell array of strings

Display the final converted cell array of strings

💡 Why This Matters

🌍 Real World

Sensors and devices often send data as text. Converting text to numbers is essential for calculations and analysis.

💼 Career

Understanding type conversion is important for data cleaning, processing, and preparing data for machine learning or reporting.

1

Create a cell array of text strings

Create a cell array called sensorData with these exact string values: '12.5', '7.8', '15.3', '9.1'.

MATLAB

% Create a cell array called sensorData with the given string values
% Your code here

Hint

Use curly braces {} to create a cell array of strings in MATLAB.

2

Create a variable for the number of elements

Create a variable called numElements and set it to the number of elements in sensorData using the length function.

MATLAB

sensorData = {'12.5', '7.8', '15.3', '9.1'};
% Create numElements to hold the number of elements in sensorData
% Your code here

Hint

Use length(sensorData) to get the number of elements in the cell array.

3

Convert the cell array of strings to a numeric array

Create a numeric array called numericData by converting each string in sensorData to a number using the str2double function inside a for loop with index i from 1 to numElements.

MATLAB

sensorData = {'12.5', '7.8', '15.3', '9.1'};
numElements = length(sensorData);
% Convert sensorData strings to numericData array
% Your code here

Hint

Use a for loop and str2double to convert each string to a number.

4

Convert numeric array back to cell array of strings and display

Create a cell array called convertedStrings by converting each number in numericData back to a string using the num2str function inside a for loop with index i from 1 to numElements. Then, display convertedStrings using disp.

MATLAB

sensorData = {'12.5', '7.8', '15.3', '9.1'};
numElements = length(sensorData);
numericData = zeros(1, numElements);
for i = 1:numElements
    numericData(i) = str2double(sensorData{i});
end
% Convert numericData back to strings and display
% Your code here

Hint

Use num2str inside a for loop to convert numbers to strings, then use disp to show the result.

Practice

1. Which MATLAB function converts a string representing a number into a numeric double type?

easy

A. str2double

B. double

C. int32

D. char

Solution

1. Step 1: Understand the input and output types

   The input is a string representing a number, and the output should be a numeric double type.

2. Step 2: Identify the correct conversion function

   str2double converts strings to double numbers, while double converts numeric types to double, int32 converts to 32-bit integers, and char converts numbers to characters.

3. Final Answer:

   str2double -> Option A

4. Quick Check:

   String to double = str2double [OK]

Hint: Use str2double for string to number conversion [OK]

Common Mistakes:

• Using double on a string causes error
• Using int32 converts to integer, not double
• Using char converts to characters, not numbers

2. Which of the following is the correct syntax to convert a numeric variable x to a 32-bit integer in MATLAB?

easy

A. convertToInt32(x)

B. int(x, 32)

C. int32(x)

D. toInt32(x)

Solution

1. Step 1: Recall MATLAB's type conversion syntax

   MATLAB uses functions named after the target type, like int32, called with parentheses around the variable.

2. Step 2: Check each option's syntax

   Only int32(x) is valid MATLAB syntax. The others are not MATLAB functions or use incorrect syntax.

3. Final Answer:

   int32(x) -> Option C

4. Quick Check:

   Correct syntax for int32 conversion = int32(x) [OK]

Hint: Use function name with parentheses for conversion [OK]

Common Mistakes:

• Using non-existent functions like convertToInt32
• Incorrect function call syntax
• Confusing with other language syntax

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

x = '123.45';
y = str2double(x);
z = int32(y);
disp(z);

medium

A. 123.45

B. '123.45'

C. Error

D. 123

Solution

1. Step 1: Convert string to double

   str2double('123.45') converts the string to numeric double 123.45.

2. Step 2: Convert double to int32

   int32(123.45) converts the double to integer by truncating the decimal part, resulting in 123.

3. Final Answer:

   123 -> Option D

4. Quick Check:

   str2double + int32 truncates decimals = 123 [OK]

Hint: int32 truncates decimals after str2double [OK]

Common Mistakes:

• Expecting int32 to round instead of truncate
• Thinking str2double returns string
• Confusing output with original string

4. Identify the error in this MATLAB code snippet:

x = 65;
y = str2double(x);
disp(y);

medium

A. str2double cannot convert numeric input

B. x should be a string for str2double

C. Missing semicolon after disp(y)

D. disp cannot display numeric values

Solution

1. Step 1: Check input type for str2double

   str2double expects a string input, but x is numeric (65).

2. Step 2: Identify the cause of error

   Passing numeric x to str2double causes unexpected behavior or error because it is not a string.

3. Final Answer:

   x should be a string for str2double -> Option B

4. Quick Check:

   str2double needs string input [OK]

Hint: str2double requires string input, not numeric [OK]

Common Mistakes:

• Passing numeric directly to str2double
• Thinking disp needs semicolon
• Believing disp can't show numbers

5. You have a cell array of strings representing numbers: data = {'10', '20.5', '30', '40.7'}. Which MATLAB code correctly converts all elements to a numeric array of doubles?

hard

A. numArray = cellfun(@str2double, data);

B. numArray = double(data);

C. numArray = int32(data);

D. numArray = str2double(data);

Solution

1. Step 1: Understand data type and conversion needed

   data is a cell array of strings; we want a numeric double array.

2. Step 2: Use cellfun with str2double

   cellfun(@str2double, data) applies str2double to each cell element, converting strings to doubles.

3. Step 3: Check other options

   double(data) and int32(data) do not work on cell arrays directly; str2double(data) expects a string, not a cell array.

4. Final Answer:

   numArray = cellfun(@str2double, data); -> Option A

5. Quick Check:

   Use cellfun with str2double for cell string arrays [OK]

Hint: Use cellfun(@str2double, cellArray) for cell string to numbers [OK]

Common Mistakes:

• Trying double or int32 on cell arrays directly
• Using str2double on cell array without cellfun
• Not converting strings inside cells individually