String comparison in MATLAB

Introduction

String comparison helps you check if two pieces of text are the same or different. This is useful when you want to make decisions based on words or sentences.

Checking if a user entered the correct password.

Comparing two names to see if they match.

Finding if a word exists in a list of words.

Sorting a list of words alphabetically.

Filtering data based on text labels.

Syntax

MATLAB

tf = strcmp(str1, str2)
tf = strcmpi(str1, str2)

strcmp compares two strings and returns logical true (1) if they are exactly the same, logical false (0) otherwise.

strcmpi does the same but ignores uppercase or lowercase differences.

Examples

Returns true because both strings are exactly the same.

MATLAB

result = strcmp('hello', 'hello')

Returns false because the case is different.

MATLAB

result = strcmp('Hello', 'hello')

Returns true because strcmpi ignores case differences.

MATLAB

result = strcmpi('Hello', 'hello')

Sample Program

This program compares two strings first with case sensitivity, then ignoring case, and prints the result.

MATLAB

str1 = 'Matlab';
str2 = 'matlab';

if strcmp(str1, str2)
    disp('Strings are exactly the same.')
elseif strcmpi(str1, str2)
    disp('Strings are the same ignoring case.')
else
    disp('Strings are different.')
end

Important Notes

Use strcmp for exact matches including case.

Use strcmpi when you want to ignore uppercase or lowercase differences.

Both functions return logical true (1) or false (0), which you can use in if statements.

Summary

String comparison checks if two texts are the same or different.

Use strcmp for case-sensitive comparison.

Use strcmpi for case-insensitive comparison.

Practice

1. Which MATLAB function is used to compare two strings with case sensitivity?

easy

A. strcmpi

B. strcmp

C. strcomp

D. strcompare

Solution

1. Step 1: Understand string comparison functions

   MATLAB provides strcmp for case-sensitive string comparison and strcmpi for case-insensitive comparison.

2. Step 2: Identify the correct function for case-sensitive comparison

   strcmp compares strings exactly, including letter case, so it is the correct choice.

3. Final Answer:

   strcmp -> Option B

4. Quick Check:

   Case-sensitive comparison = strcmp [OK]

Hint: Use strcmp for exact case-sensitive string checks [OK]

Common Mistakes:

• Confusing strcmp with strcmpi
• Using non-existent functions like strcomp
• Assuming strcmpi is case-sensitive

2. Which of the following is the correct syntax to compare two strings s1 and s2 ignoring case in MATLAB?

easy

A. strcmpi(s1 == s2)

B. strcmp(s1, s2)

C. strcmpi(s1, s2)

D. strcmp(s1 == s2)

Solution

1. Step 1: Recall syntax for case-insensitive comparison

   strcmpi compares two strings ignoring case and takes two string inputs as separate arguments.

2. Step 2: Identify correct syntax

   strcmpi(s1, s2) uses strcmpi with two string arguments correctly. Options C and D incorrectly use '==' inside the function, which is invalid.

3. Final Answer:

   strcmpi(s1, s2) -> Option C

4. Quick Check:

   Case-insensitive syntax = strcmpi(s1, s2) [OK]

Hint: Use strcmpi(s1, s2) for ignoring case in string comparison [OK]

Common Mistakes:

• Using '==' inside strcmp or strcmpi
• Mixing up strcmp and strcmpi
• Passing strings as one argument with '=='

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

s1 = "Hello";
s2 = "hello";
result = strcmp(s1, s2);
disp(result);

medium

A. "true"

B. 1

C. Error

D. 0

Solution

1. Step 1: Understand strcmp behavior

   strcmp compares strings with case sensitivity. "Hello" and "hello" differ in case.

2. Step 2: Evaluate strcmp result

   Since the strings differ in case, strcmp returns logical 0 (false), which disp prints as 0.

3. Final Answer:

   0 -> Option D

4. Quick Check:

   Case-sensitive mismatch = 0 [OK]

Hint: strcmp returns 0 if cases differ exactly [OK]

Common Mistakes:

• Assuming strcmp ignores case
• Expecting output '1' for different case
• Confusing output with string 'true'

4. Identify the error in this MATLAB code snippet for case-insensitive string comparison:

s1 = "Test";
s2 = "test";
if strcmpi(s1 == s2)
    disp('Match');
end

medium

A. Using '==' inside strcmpi causes an error

B. Missing semicolon after disp statement

C. strcmpi cannot compare strings

D. Strings must be converted to char arrays first

Solution

1. Step 1: Analyze the use of '==' inside strcmpi

   The expression s1 == s2 compares strings element-wise, returning a logical array, not a string.

2. Step 2: Understand strcmpi input requirements

   strcmpi expects two string inputs, not a logical array. Using '==' inside causes a syntax or runtime error.

3. Final Answer:

   Using '==' inside strcmpi causes an error -> Option A

4. Quick Check:

   strcmpi needs strings, not logical arrays [OK]

Hint: Do not use '==' inside strcmpi; pass strings directly [OK]

Common Mistakes:

• Using '==' inside strcmpi
• Thinking strcmpi compares logical arrays
• Ignoring input type requirements

5. You want to compare two cell arrays of strings C1 = {'Apple', 'Banana', 'Cherry'} and C2 = {'apple', 'banana', 'cherry'} ignoring case. Which MATLAB code correctly returns a logical array indicating matches?

hard

A. cellfun(@strcmpi, C1, C2)

B. strcmpi(C1{:}, C2{:})

C. cellfun(@strcmp, C1, C2)

D. strcmp(C1, C2)

Solution

1. Step 1: Understand cell array string comparison

   To compare each pair of strings in cell arrays element-wise, use cellfun with a comparison function.

2. Step 2: Choose case-insensitive comparison

   strcmpi ignores case, so cellfun(@strcmpi, C1, C2) applies it element-wise correctly.

3. Step 3: Why other options fail

   cellfun(@strcmp, C1, C2) uses case-sensitive strcmp. strcmpi(C1{:}, C2{:}) unpacks cells into multiple arguments, causing a "too many input arguments" error. strcmp(C1, C2) is case-sensitive.

4. Final Answer:

   cellfun(@strcmpi, C1, C2) -> Option A

5. Quick Check:

   Use cellfun with strcmpi for cell array case-insensitive comparison [OK]

Hint: Use cellfun(@strcmpi, C1, C2) for cell array case-insensitive compare [OK]

Common Mistakes:

• Using strcmp instead of strcmpi for ignoring case
• Unpacking cell arrays with strcmpi(C1{:}, C2{:})
• Not using cellfun for element-wise comparison