String replacement in MATLAB - Mini Project: Build & Apply

String replacement

📖 Scenario: You work in a small publishing company. You have a text with some outdated words that need to be replaced with new ones before printing.

🎯 Goal: You will create a MATLAB program that replaces specific words in a text string with new words using string replacement.

📋 What You'll Learn

Create a string variable with the exact given text

Create a variable for the word to find

Use the replace function to replace the word

Print the updated string

💡 Why This Matters

🌍 Real World

Replacing outdated or incorrect words in text documents before publishing.

💼 Career

Useful for roles in data cleaning, text processing, and software that handles user content.

1

Create the original text string

Create a string variable called originalText with the exact value: 'The colour of the sky is blue.'

MATLAB

% Create the string variable originalText with the given sentence
% Your code here

Hint

Use single quotes to create a string in MATLAB.

2

Create the word to find

Create a string variable called wordToFind and set it to 'colour'.

MATLAB

originalText = 'The colour of the sky is blue.';
% Create the variable wordToFind with the value 'colour'
% Your code here

Hint

Remember to use single quotes for strings in MATLAB.

3

Replace the word in the text

Create a new string variable called updatedText by replacing wordToFind in originalText with 'color' using the replace function.

MATLAB

originalText = 'The colour of the sky is blue.';
wordToFind = 'colour';
% Replace wordToFind with 'color' in originalText and store in updatedText
% Your code here

Hint

The syntax is replace(originalString, oldWord, newWord).

4

Display the updated text

Use disp to print the updatedText variable.

MATLAB

originalText = 'The colour of the sky is blue.';
wordToFind = 'colour';
updatedText = replace(originalText, wordToFind, 'color');
% Display the updatedText
% Your code here

Hint

Use disp(variable) to show the string in MATLAB.

Practice

1. What does the MATLAB function strrep('hello world', 'world', 'MATLAB') do?

easy

A. Replaces 'world' with 'MATLAB' resulting in 'hello MATLAB'

B. Removes the word 'world' from the string

C. Returns an error because 'world' is not a variable

D. Converts the entire string to uppercase

Solution

1. Step 1: Understand strrep function

   The function strrep replaces all occurrences of a substring with a new substring in a given string.

2. Step 2: Apply strrep to the example

   It replaces 'world' with 'MATLAB' in 'hello world', resulting in 'hello MATLAB'.

3. Final Answer:

   Replaces 'world' with 'MATLAB' resulting in 'hello MATLAB' -> Option A

4. Quick Check:

   strrep('hello world', 'world', 'MATLAB') = 'hello MATLAB' [OK]

Hint: Remember: strrep replaces all matching substrings [OK]

Common Mistakes:

• Thinking strrep removes substrings instead of replacing
• Confusing strrep with uppercase functions
• Assuming strrep only works on variables

2. Which of the following is the correct syntax to replace all occurrences of 'cat' with 'dog' in the string text = 'cat and cat'?

easy

A. replace(text, cat, dog)

B. strrep(text, 'cat', 'dog')

C. text.replace('cat', 'dog')

D. str_replace(text, 'cat', 'dog')

Solution

1. Step 1: Recall MATLAB string replacement syntax

   In MATLAB, the function to replace substrings is strrep(originalStr, oldSubstr, newSubstr).

2. Step 2: Match the correct syntax

   strrep(text, 'cat', 'dog') uses strrep correctly with the right order of arguments.

3. Final Answer:

   strrep(text, 'cat', 'dog') -> Option B

4. Quick Check:

   Correct MATLAB syntax for string replacement is strrep() [OK]

Hint: Use strrep(original, old, new) for replacements [OK]

Common Mistakes:

• Using Python or other language syntax by mistake
• Misspelling function names
• Using dot notation which MATLAB strings don't support

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

str = 'apple banana apple';
newStr = strrep(str, 'apple', 'orange');
disp(newStr);

medium

A. orange banana apple

B. apple banana orange

C. orange banana orange

D. apple banana apple

Solution

1. Step 1: Identify the original string and replacement

   The original string is 'apple banana apple'. The function replaces all 'apple' with 'orange'.

2. Step 2: Apply strrep to replace all occurrences

   Both 'apple' words are replaced, resulting in 'orange banana orange'.

3. Final Answer:

   orange banana orange -> Option C

4. Quick Check:

   strrep replaces all matches, not just first [OK]

Hint: strrep replaces every match, not just one [OK]

Common Mistakes:

• Replacing only the first occurrence
• Confusing strrep with regex functions
• Expecting original string unchanged

4. The following MATLAB code is intended to replace 'dog' with 'cat' in the string text = 'dog and dog'. What is the error?

text = 'dog and dog';
newText = strrep(text, dog, cat);
disp(newText);

medium

A. Missing quotes around 'dog' and 'cat' causing an error

B. strrep cannot replace substrings in character arrays

C. disp cannot display strings

D. No error, code runs correctly

Solution

1. Step 1: Check argument types in strrep

   In MATLAB, substrings must be given as strings or character arrays enclosed in quotes.

2. Step 2: Identify missing quotes causing error

   The code uses dog and cat without quotes, which MATLAB treats as variables, causing an error.

3. Final Answer:

   Missing quotes around 'dog' and 'cat' causing an error -> Option A

4. Quick Check:

   String literals need quotes in strrep arguments [OK]

Hint: Always quote substrings in strrep arguments [OK]

Common Mistakes:

• Forgetting quotes around substrings
• Assuming variables are strings automatically
• Thinking disp cannot show strings

5. Given a string array words = ["red", "blue", "red", "green"], which MATLAB code replaces all occurrences of "red" with "yellow" correctly?

hard

A. newWords = strrep(words, red, 'yellow');

B. newWords = strrep(words, "red", yellow);

C. newWords = strrep(words, red, yellow);

D. newWords = replace(words, 'red', 'yellow');

Solution

1. Step 1: Understand string array replacement functions

   For string arrays, MATLAB's replace function works correctly, while strrep works on character arrays.

2. Step 2: Identify the correct function and syntax

   newWords = replace(words, 'red', 'yellow'); uses replace with proper quotes, which replaces all "red" with "yellow" in the string array.

3. Final Answer:

   newWords = replace(words, 'red', 'yellow'); -> Option D

4. Quick Check:

   Use replace() for string arrays, strrep() for char arrays [OK]

Hint: Use replace() for string arrays, strrep() for char arrays [OK]

Common Mistakes:

• Using strrep on string arrays (causes error)
• Forgetting quotes around substrings
• Confusing variable names with strings