strrep — Replace non-overlapping substring occurrences in text inputs with MATLAB-compatible container behavior.
strrep(str, old, new) replaces every non-overlapping occurrence of old with new. It supports MATLAB-compatible string, char, and cellstr-style inputs with element-wise replacement semantics.
Syntax
newStr = strrep(str, old, new)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
str | Any | Yes | — | Input text (string/char/cell). |
old | Any | Yes | — | Pattern text scalar (string or char row). |
new | Any | Yes | — | Replacement text scalar matching old's data type family. |
Returns
| Name | Type | Description |
|---|---|---|
newStr | Any | Text with pattern occurrences replaced, preserving input container kind. |
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:strrep:InvalidInput | First argument is not a string array, char array, or cell array of text scalars. | strrep: first argument must be a string array, character array, or cell array of character vectors |
RunMat:strrep:PatternType | old/new arguments are not string scalars or character vectors. | strrep: old and new must be string scalars or character vectors |
RunMat:strrep:PatternMismatch | old and new are different text data families (string vs char). | strrep: old and new must be the same data type |
RunMat:strrep:CellElement | Cell input contains non-text elements or non-row char arrays. | strrep: cell array elements must be string scalars or character vectors |
RunMat:strrep:InternalError | Internal output container construction failed. | strrep: internal error |
How strrep works
- String scalars remain strings. Missing string values (
<missing>) propagate unchanged. - String arrays are processed element-wise while preserving their full shape and orientation.
- Character arrays are handled row by row. Rows expand or shrink as needed and are padded with spaces so the result stays a rectangular char array, just like MATLAB.
- Cell arrays must contain character vectors or string scalars. The result is a cell array of identical size where each element has had the replacement applied.
- The
oldandnewarguments must be string scalars or character vectors of the same data type. oldcan be empty. In that case,strrepinsertsnewbefore the first character, between existing characters, and after the final character.- Integer values in any of the three text roles are rejected rather than treated as character codes or formatted numbers.
Does RunMat run strrep on the GPU?
strrep computes replacements on host text and returns a host text container of the corresponding kind. Numeric resident values reject before provider access rather than being gathered and implicitly converted to text.
GPU memory and residency
No. strrep accepts host text and returns host text. Provider-resident numeric values are unsupported and reject before access.
Examples
Replacing a word inside a string scalar
txt = "RunMat turbo mode";
result = strrep(txt, "turbo", "accelerate")Expected output:
result = "RunMat accelerate mode"Updating every element of a string array
labels = ["GPU planner", "CPU planner"];
updated = strrep(labels, "planner", "pipeline")Expected output:
updated = 2×1 string
"GPU pipeline"
"CPU pipeline"Preserving rectangular shape in character arrays
chars = char("alpha", "beta ");
out = strrep(chars, "a", "A")Expected output:
out =
2×5 char array
'AlphA'
'betA 'Applying replacements inside a cell array of character vectors
C = {'Kernel Fusion', 'GPU Planner'};
renamed = strrep(C, ' ', '_')Expected output:
renamed = 1×2 cell array
{'Kernel_Fusion'} {'GPU_Planner'}Inserting text with an empty search pattern
stub = "abc";
expanded = strrep(stub, "", "-")Expected output:
expanded = "-a-b-c-"Leaving missing string values untouched
vals = ["RunMat", "<missing>", "Accelerate"];
out = strrep(vals, "RunMat", "RUNMAT")Expected output:
out = 1×3 string
"RUNMAT" <missing> "Accelerate"Replacing substrings gathered from GPU inputs
g = gpuArray("native-code");
host = strrep(g, "code", "path")Expected output:
host = "native-path"Using strrep with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how strrep changes the result.
Run a small strrep example, explain the result, then change one input and compare the output.
FAQ
Which input types does strrep accept?⌄
String scalars, string arrays, character vectors, character arrays, and cell arrays of character vectors. The old and new arguments must be string scalars or character vectors of the same data type.
Does strrep support multiple search terms at once?⌄
No. Use the newer replace builtin if you need to substitute several search terms in a single call.
How does strrep handle missing strings?⌄
Missing string scalars remain <missing> and are returned unchanged, even when the search pattern matches ordinary text.
Will rows of a character array stay aligned?⌄
Yes. Each row is replaced individually, then padded with spaces so that the overall array stays rectangular, matching MATLAB exactly.
What happens when old is empty?⌄
RunMat mirrors MATLAB: new is inserted before the first character, between every existing character, and after the last character.
Does strrep run on the GPU?⌄
No GPU text representation is supported. Numeric GPU values are not text and reject before provider access; convert supported host data to strings explicitly before calling strrep.
Can I mix strings and character vectors for old and new?⌄
No. MATLAB requires old and new to share the same data type. RunMat enforces the same rule and raises a descriptive error when they differ.
How do I replace text stored inside cell arrays?⌄
strrep traverses the cell array, applying the replacement to each character vector or string scalar element and returning a cell array of the same shape.
Related Strings functions
Transform
append · deblank · erase · eraseBetween · erasePunctuation · eraseURLs · extractAfter · extractBefore · extractBetween · insertAfter · insertBefore · join · lower · pad · replace · replaceBetween · reverse · split · splitlines · strcat · strip · strjoin · strjust · strsplit · strtrim · upper
Text Analytics
addDependencyDetails · addEntityDetails · addLemmaDetails · addPartOfSpeechDetails · addSentenceDetails · addTypeDetails · bagOfNgrams · bagOfWords · cosineSimilarity · doc2sequence · encode · extractFileText · extractHTMLText · fastTextWordEmbedding · findElement · getAttribute · htmlTree · ind2word · isVocabularyWord · normalizeWords · readWordEmbedding · removeLongWords · removeShortWords · removeStopWords · removeWords · stopWords · tokenDetails · tokenizedDocument · trainWordEmbedding · vaderSentimentScores · vec2word · word2ind · word2vec · wordEncoding · writeWordEmbedding
Core
blanks · char · compose · convertCharsToStrings · convertContainedStringsToChars · convertStringsToChars · genvarname · int2str · isletter · isspace · isStringScalar · isstrprop · mat2str · native2unicode · newline · num2str · sprintf · sscanf · str2double · str2num · strcmp · strcmpi · string · string.empty · strings · strlength · strncmp · strncmpi · strtok · unicode2native
Search
contains · endsWith · matches · startsWith · strfind
Pattern
digitsPattern · lettersPattern · pattern · regexpPattern · textBoundary · wildcardPattern
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how strrep is executed, line by line, in Rust.
- View the source for strrep in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
RunMat is an open-source runtime that executes MATLAB-syntax code blazing on any GPU. It is licensed under the Apache 2.0 license.
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