String replacement in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function in MATLAB is commonly used to replace parts of a string?

The strrep function is used to replace occurrences of a substring within a string with another substring.

beginner

How does strrep work in MATLAB?

It takes three inputs: the original string, the substring to find, and the substring to replace it with. It returns a new string with all occurrences replaced.

beginner

Example: What is the result of strrep('hello world', 'world', 'MATLAB')?

The output is 'hello MATLAB' because the substring 'world' is replaced by 'MATLAB'.

intermediate

Can strrep replace multiple occurrences of a substring in MATLAB?

Yes, strrep replaces all occurrences of the specified substring in the original string.

beginner

What happens if the substring to replace is not found in the original string when using strrep?

The original string is returned unchanged because there is nothing to replace.

Which MATLAB function replaces all occurrences of a substring within a string?

A stringreplace

B strrep

C substitute

D replaceall

The correct function is strrep. The others do not exist in MATLAB.

What does strrep('apple pie', 'pie', 'cake') return?

A 'apple cake'

B 'apple pie'

C 'cake pie'

D 'applecake'

It replaces 'pie' with 'cake', so the result is 'apple cake'.

If the substring to replace is not found, what does strrep do?

A Returns the original string unchanged

B Returns an error

C Returns an empty string

D Replaces the whole string

strrep returns the original string unchanged if the substring is not found.

Can strrep replace multiple occurrences of a substring?

A No, it replaces only the last occurrence

B No, it replaces only the first occurrence

C It depends on an additional parameter

D Yes, it replaces all occurrences

strrep replaces all occurrences of the substring in the string.

What is the correct syntax for strrep?

A strrep(new, old, original)

B strrep(old, new, original)

C strrep(original, old, new)

D strrep(original, new, old)

The syntax is strrep(originalString, oldSubstring, newSubstring).

Explain how to replace a substring in a MATLAB string using strrep.

Think about the inputs and output of the function.

Describe what happens when the substring to replace does not exist in the original string in MATLAB's strrep.

Consider what the function returns if it finds nothing to replace.

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