width — Return the number of table variables or array columns.
width(T) returns the number of variables in a table or the number of columns in an array.
Syntax
n = width(T)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
T | Any | Yes | — | Table input. |
Returns
| Name | Type | Description |
|---|---|---|
n | IntegerScalar | Count. |
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:table:InvalidArgument | Arguments or table metadata are invalid. | table: invalid argument |
RunMat:table:InvalidIndex | Table indexing is invalid. | table: invalid index |
RunMat:table:InvalidVariable | A table variable name or value is invalid. | table: invalid variable |
RunMat:readtable:IOError | readtable cannot open or read the requested file. | readtable: file read failed |
RunMat:readtable:UnsupportedFileType | readtable receives a file type outside the text or spreadsheet import backends. | readtable: unsupported file type |
How width works
- For a table, the result is its variable count. For an ordinary array, the result is the size of its second dimension.
- All eight native integer classes follow the same structural rule; their elements are neither converted nor inspected.
- The result is a host
doublescalar. - For a resident numeric array, RunMat reads the column count directly from handle shape metadata without gathering payload data.
Does RunMat run width on the GPU?
width does not dispatch a numerical kernel or gather the input. It returns the second handle dimension as a host double scalar.
GPU memory and residency
Numeric payloads remain resident; only shape metadata is read.
Example
Count array columns
n = width(uint16(zeros(3, 5)))Expected output:
n = 5Using width with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how width changes the result.
Run a small width example, explain the result, then change one input and compare the output.
FAQ
Does width gather a gpuArray?⌄
No. RunMat obtains the column count from resident shape metadata and returns a host double scalar.
Related Table functions
array2table · array2timetable · categorical · cell2table · dictionary · groupsummary · head · height · iscategorical · isordinal · istable · istimetable · ordinal · pivot · rowfilter · struct2table · table · table2array · table2cell · table2struct · table2timetable · timerange · timetable · timetable2table · uitable · vartype
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how width is executed, line by line, in Rust.
- View the source for width 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.
- RunMat automatically optimizes your math for GPU execution on Apple, Nvidia, and AMD hardware. No code changes needed. Simulations that took hours now take minutes.
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