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CategoryStructs: Core

isfield — Test whether a struct or struct array defines specific field names.

tf = isfield(S, name) returns a logical value that indicates whether the struct S defines the field name. When name is a string array or a cell array of names, isfield returns a logical array with the same size, reporting the result for each requested field.

How does the isfield function behave in MATLAB / RunMat?

  • Works with scalar structs and struct arrays created with struct, load, or similar builtins.
  • Accepts character vectors, string scalars, string arrays, or cell arrays containing character vectors and/or string scalars for the name argument.
  • Returns a scalar logical (true/false) when name is a single string or char vector.
  • Returns a logical array that matches the size of name when it is a string array or cell array.
  • If the first argument is not a struct or struct array, the result is false (or a logical array of false values) without raising an error.
  • Empty struct arrays yield false for every queried name because they do not carry field metadata once the elements have been removed.

GPU behavior

isfield performs metadata checks entirely on the host. It never gathers or copies GPU tensors that may be stored inside the struct; it only inspects the host-side descriptors that record field names. No acceleration provider hooks are required.

GPU residency

isfield is metadata-only. It neither moves nor inspects the contents of GPU tensors that might live inside the struct. You do not need to call gpuArray or gather to use the builtin; residency is preserved automatically.

Examples of using isfield in MATLAB / RunMat

Checking whether a struct defines a single field

s = struct("name", "Ada", "score", 42);
hasScore = isfield(s, "score")

Expected output:

hasScore =
  logical
   1

Testing multiple field names at once

s = struct("name", "Ada", "score", 42);
names = {"name", "department"; "score", "email"};
mask = isfield(s, names)

Expected output:

mask =
  2×2 logical array
     1     0
     1     0

Inspecting a struct array that shares a common schema

people = struct("name", {"Ada", "Grace"}, "id", {101, 102});
idxMask = isfield(people, ["id", "department"])

Expected output:

idxMask =
  1×2 logical array
     1     0

Using isfield before accessing optional configuration fields

cfg = struct("mode", "fast");
if ~isfield(cfg, "rate")
    cfg.rate = 60;
end

Mixing string scalars and character vectors in a cell array

opts = struct("Solver", "cg", "MaxIter", 200);
queries = {"Solver", "Tolerances"; "MaxIter", "History"};
present = isfield(opts, queries)

Behaviour when the input is not a struct

value = 42;
tf = isfield(value, "anything")

Expected output:

tf =
  logical
   0

FAQ

What argument types does isfield accept for field names?

Character vectors, string scalars, string arrays, and cell arrays that contain character vectors or string scalars. Passing other types raises an error.

Does isfield error when the first input is not a struct?

No. It returns false (or a logical array of false) to mirror MATLAB's behaviour. Use isstruct if you need to guard against non-struct inputs before calling isfield.

How do struct arrays affect the result?

Every element of the struct array must contain the queried field. If any element is missing the field, the result is false for that name.

What happens with empty struct arrays?

Empty struct arrays do not retain field metadata in RunMat yet, so isfield returns false for all queries. This matches MATLAB when the struct has no defined fields.

Are field name comparisons case-sensitive?

Yes. Field names are compared using exact, case-sensitive matches, just like MATLAB.

Does isfield gather GPU data?

No. The builtin only inspects field metadata and leaves GPU-resident tensors untouched.

See also

fieldnames, struct, getfield, setfield

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