How Can Replacing Characters In A String?

In MATLAB, the modern and most versatile way to replace characters or substrings is using the replace() function: newStr = replace(str, oldText, newText). For advanced pattern matching (such as replacing digits, symbols, or whitespace), use regexprep(), and for position-specific modifications, use replaceBetween() or direct character vector indexing.

Top 5 Methods to Replace Characters in MATLAB

1. Modern Substring Replacement via replace() (Recommended)

The replace() function works seamlessly on string scalars, string arrays, and character vectors, and supports replacing multiple words simultaneously:

% Basic single replacement
originalStr = "MATLAB is slow for big data.";
updatedStr = replace(originalStr, "slow", "fast");
disp(updatedStr); % Output: "MATLAB is fast for big data."

% Multiple simultaneous replacements using array matching
rawText = "The red car parked next to the red building.";
cleanText = replace(rawText, ["red", "car"], ["blue", "truck"]);
disp(cleanText); % Output: "The blue truck parked next to the blue building."

% Vectorized replacement across entire string arrays
fileNames = ["sensor_test_v1.csv", "sensor_test_v2.csv", "sensor_test_v3.csv"];
correctedFiles = replace(fileNames, "test", "production");
disp(correctedFiles);

2. Regular Expression Replacement via regexprep()

Use regexprep() when you need pattern matching, such as sanitizing filenames, replacing numbers, or removing special symbols:

% Replace all digits (\d+) with an 'X'
serialCode = "Device-Model-9843-Batch-2024";
maskedCode = regexprep(serialCode, '\d+', 'XXXX');
disp(maskedCode); % Output: "Device-Model-XXXX-Batch-XXXX"

% Replace multiple spaces and tabs with a single space
messyText = "MATLAB    Simulink       Control";
cleanSpacing = regexprep(messyText, '\s+', ' ');
disp(cleanSpacing); % Output: "MATLAB Simulink Control"

% Remove all non-alphanumeric special characters
rawInput = "User#123_Profile$Data@2026!";
sanitized = regexprep(rawInput, '[^a-zA-Z0-9_]', '');
disp(sanitized); % Output: "User123_ProfileData2026"

3. Positional Replacement via replaceBetween()

If you want to replace characters between specific delimiter boundaries or fixed index ranges without modifying the rest of the text, use replaceBetween():

% Replace text inside parentheses
equation = "y = sin(theta_old) + cos(theta_old)";
newEquation = replaceBetween(equation, "(", ")", "x_new");
disp(newEquation); % Output: "y = sin(x_new) + cos(x_new)"

% Replace characters by numerical index range (positions 8 to 12)
code = "ABCDEF-OLDDATA-XYZ";
updatedCode = replaceBetween(code, 8, 14, "NEWVAL");
disp(updatedCode); % Output: "ABCDEF-NEWVAL-XYZ"

4. Direct Indexing on Character Arrays

For character vectors (enclosed in single quotes '...'), you can directly modify characters by their 1-based numerical index:

% Define character array
charVec = 'Python';

% Replace first letter directly
charVec(1) = 'M';
disp(charVec); % Output: 'Mython'

% Replace a slice of characters
charVec(1:3) = 'MAT';
disp(charVec); % Output: 'MATlon'

5. Removing Characters Completely via erase()

To delete characters without inserting a replacement, use erase() instead of replacing with an empty string:

phoneNum = "+1 (555) 234-5678";
cleanDigits = erase(phoneNum, ["+", "(", ")", " ", "-"]);
disp(cleanDigits); % Output: "15552345678"

Comparison of String Replacement Functions

Key Best Practices

• Use String Objects: Prefer double-quoted strings ("text") over single-quoted character arrays ('text') in modern MATLAB scripts for automatic vectorization and superior performance.
• Case Sensitivity: replace() is case-sensitive by default. If you need case-insensitive replacements, use regexprep(str, 'pattern', 'new', 'ignorecase').