String replacement in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to replace all occurrences of 'cat' with 'dog' in the string.

MATLAB

str = 'The cat sat on the mat.';
newStr = strrep(str, 'cat', [1]);

Drag options to blanks, or click blank then click option'

A'dog'

B'rat'

C'bat'

D'cow'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around the replacement string.

Using the wrong function for replacement.

The strrep function replaces all occurrences of the second argument with the third argument in the string.

2fill in blank

medium

Complete the code to replace all spaces with underscores in the string.

MATLAB

text = 'hello world example';
result = strrep(text, [1], '_');

Drag options to blanks, or click blank then click option'

A'-'

B' '

C'_'

D','

Attempts:

3 left

💡 Hint

Common Mistakes

Using '_' as the substring to replace instead of the replacement.

Forgetting to use quotes around the space.

To replace spaces, you specify the space character ' ' as the substring to replace.

3fill in blank

hard

Fix the error in the code to replace 'apple' with 'orange' in the string.

MATLAB

fruit = 'apple pie';
newFruit = strrep(fruit, 'apple', [1]);

Drag options to blanks, or click blank then click option'

A'orange'

Borange

C'apple'

Dorange'

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the replacement string.

Using double quotes instead of single quotes.

The replacement string must be enclosed in single quotes to be recognized as a string.

4fill in blank

hard

Fill both blanks to replace 'dog' with 'cat' and 'mouse' with 'rat' in the string.

MATLAB

sentence = 'The dog chased the mouse.';
step1 = strrep(sentence, [1], 'cat');
result = strrep(step1, [2], 'rat');

Drag options to blanks, or click blank then click option'

A'dog'

B'cat'

C'mouse'

D'rat'

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of replacements.

Replacing the wrong substrings.

First replace 'dog' with 'cat', then replace 'mouse' with 'rat' using strrep.

5fill in blank

hard

Fill all three blanks to create a dictionary of words and their lengths, but only include words longer than 3 letters.

MATLAB

words = {'cat', 'elephant', 'dog', 'mouse'};
lengths = containers.Map();
for i = 1:length(words)
    word = words{i};
    if length(word) [1] 3
        lengths([2]) = [3];
    end
end

Drag options to blanks, or click blank then click option'

A>

Bword

Clength(word)

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Using the length as the key instead of the word.

We check if the word length is greater than 3, then add the word as key and its length as value to the map.

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