`structfun` — Apply a function to each field of a scalar struct.

structfun(func, S) applies func to each field value of scalar struct S. By default callback results must be scalar-uniform and are packed into a column array in field order.

Syntax

A = structfun(func, S)
A = structfun(func, S, "UniformOutput", tf)
A = structfun(func, S, "ErrorHandler", errfunc)
A = structfun(func, S, "UniformOutput", tf, "ErrorHandler", errfunc)

Inputs

Name	Type	Required	Default	Description
`func`	`Any`	Yes	—	Function handle or builtin/function name.
`S`	`Any`	Yes	—	Scalar struct input.
`UniformOutput`	`StringScalar`	Yes	`"UniformOutput"`	Name-value key for uniform output mode.
`tf`	`LogicalArray`	Yes	`true`	Whether callback outputs must be scalar-uniform.
`ErrorHandler`	`StringScalar`	Yes	`"ErrorHandler"`	Name-value key for callback error handler.
`errfunc`	`Any`	Yes	—	Error handler function handle or name.

Returns

Name	Type	Description
`A`	`Any`	Mapped callback outputs.

Returned values from structfun depend on how many outputs the caller requests.

Errors

Identifier	When	Message
`RunMat:structfun:InvalidInput`	Input callback, struct argument, or name-value forms are invalid.	`structfun: invalid input arguments`
`RunMat:structfun:NotScalarStruct`	Second argument is not a scalar struct.	`structfun: second input must be a scalar struct`
`RunMat:structfun:Internal`	Internal field vector materialisation fails.	`structfun: internal error`
`RunMat:structfun:UniformOutput`	UniformOutput mode requirements are violated.	`structfun: uniform output contract violated`
`RunMat:structfun:FunctionError`	Callback execution or callback output arity fails.	`structfun: callback execution error`

How `structfun` works

The second input must be a scalar struct. Struct arrays are rejected rather than flattened implicitly.
Callback execution uses RunMat's feval path, so function handles, semantic closures, requested output count, UniformOutput, ErrorHandler, and GPU gather behavior follow ordinary callback invocation semantics.
With "UniformOutput", true (default), every callback result must be scalar numeric, logical, or complex; results are packed into an N-by-1 array where N is the number of fields.
With "UniformOutput", false, callback outputs may have mixed types or sizes and are returned as a scalar struct preserving the input field names.
When multiple outputs are requested, each callback must return that many outputs; structfun collects each output independently.
"ErrorHandler", handler receives an error struct followed by the field value that triggered the failure.

Does RunMat run `structfun` on the GPU?

structfun is a host operation. GPU-resident field values are gathered before the callback runs and outputs are host-resident today.

Examples

Compute the length of each struct field

S = struct('a', 1:3, 'b', 10:11);
A = structfun(@length, S)

Expected output:

A =
     3
     2

Collect mixed callback outputs in a struct

S = struct('name', 'runmat', 'flag', true);
C = structfun(@class, S, 'UniformOutput', false)

Expected output:

C =
  struct with fields:
    name: 'char'
    flag: 'logical'

Using `structfun` with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how structfun changes the result.

Run a small structfun example, explain the result, then change one input and compare the output.

FAQ

Does structfun modify the input struct?⌄

No. It reads the field values, invokes the callback, and returns a new array or cell array.

Can structfun return strings or structs?⌄

Yes, when "UniformOutput" is false. The result is a scalar struct with the same field names as the input. Uniform output mode accepts only scalar numeric, logical, or complex callback results.

Are GPU field values supported?⌄

Yes. GPU-resident field values are gathered before callback invocation; outputs are host-resident today.

Can structfun collect multiple callback outputs?⌄

Yes. When callers request multiple outputs, RunMat requests the same number from every callback invocation and returns one collected output per callback output.

fieldnames · getfield · isfield · orderfields · rmfield · setfield · struct

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how structfun is executed, line by line, in Rust.

View the source for structfun 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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structfun — Apply a function to each field of a scalar struct.