grp2idx — Create an index vector from a grouping variable.
g = grp2idx(s) maps a grouping variable to one-based group indices, with missing entries mapped to NaN.
Syntax
varargout = groupingBuiltin(args...)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
args | Any | Variadic | — | MATLAB-compatible arguments. |
Returns
| Name | Type | Description |
|---|---|---|
varargout | Any | Builtin outputs. |
Returned values from grp2idx depend on how many outputs the caller requests.
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:grouping:InvalidInput | Inputs are malformed, have incompatible lengths, or request unsupported grouped output. | grouping builtin: invalid input |
RunMat:grouping:CallbackFailed | A grouped callback fails or returns incompatible outputs. | grouping builtin: callback failed |
RunMat:grouping:TooLarge | The requested dense or combinatorial output exceeds RunMat's materialization limit. | grouping builtin: output is too large |
How grp2idx works
- Supports numeric, logical, string, cell, and categorical grouping vectors.
- Additional outputs return group label strings in sorted group order.
Example
Index groups
g = grp2idx(["b";"a";"b"])Expected output:
g = [2; 1; 2]Using grp2idx with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how grp2idx changes the result.
Run a small grp2idx example, explain the result, then change one input and compare the output.
Related Array functions
Grouping
accumarray · combinations · discretize · findgroups · groupcounts · splitapply
Sorting Sets
argsort · intersect · ismember · ismembertol · issorted · issortedrows · setdiff · setxor · sort · sortrows · union · unique
Shape
blkdiag · cat · circshift · diag · flip · fliplr · flipud · horzcat · ipermute · kron · permute · repelem · repmat · reshape · rot90 · squeeze · toeplitz · tril · triu · vertcat
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how grp2idx is executed, line by line, in Rust.
- View the source for grp2idx in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
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