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CategoryStrings: Transform

What does the upper function do in MATLAB / RunMat?

upper(text) converts every alphabetic character in text to uppercase. It accepts string scalars, string arrays, character arrays, and cell arrays of character vectors, mirroring MATLAB behaviour. Non-alphabetic characters are returned unchanged.

How does the upper function behave in MATLAB / RunMat?

  • String inputs stay as strings. String arrays preserve their size, orientation, and missing values.
  • Character arrays are processed row by row. The result remains a rectangular char array; if any row grows after uppercasing (for example 'ß' → "SS"), the array widens and shorter rows are padded with spaces.
  • Cell arrays must contain string scalars or character vectors. The result is a cell array of the same size with each element converted to uppercase; other types raise MATLAB-compatible errors.
  • Missing string scalars (string(missing)) remain <missing> so downstream code behaves like MATLAB.
  • Inputs that are numeric, logical, structs, or GPU tensors raise MATLAB-compatible type errors.

upper Function GPU Execution Behaviour

upper executes on the CPU. Text values currently reside in host memory, so providers do not offer device kernels for this builtin. When you pass a container that still holds GPU handles (for example, a struct whose string fields were gathered lazily), RunMat gathers those handles before performing the conversion. If you store characters as numeric code points on the GPU, gather and convert them to text before calling upper.

GPU residency in RunMat (Do I need gpuArray?)

RunMat keeps text data in host memory, so you typically work with ordinary string and character arrays. When text originates from GPU computations (for example, numeric code points produced by kernels), gather those values to the host and convert them to text before calling upper.

Examples of using the upper function in MATLAB / RunMat

Convert a string scalar to uppercase

txt = "RunMat";
result = upper(txt);

Expected output:

result = "RUNMAT"

Uppercase each element of a string array

labels = ["north" "South"; "East" "west"];
uppered = upper(labels);

Expected output:

uppered = 2×2 string
    "NORTH"    "SOUTH"
    "EAST"     "WEST"

Uppercase character array rows while preserving shape

animals = char("cat", "doge");
result = upper(animals);

Expected output:

result =

  2×4 char array

    'CAT '
    'DOGE'

Uppercase a cell array of character vectors

C = {'hello', 'World'};
out = upper(C);

Expected output:

out = 1×2 cell array
    {'HELLO'}    {'WORLD'}

Keep missing strings as missing

vals = ["data", string(missing), "gpu"];
converted = upper(vals);

Expected output:

converted = 1×3 string
    "DATA"    <missing>    "GPU"

Handle text stored on a GPU input

codes = gpuArray(uint16('runmat'));
txt = char(gather(codes));
result = upper(txt);

Expected output:

result = 'RUNMAT'

FAQ

Does upper change non-alphabetic characters?

No. Digits, punctuation, whitespace, and symbols remain untouched. Only alphabetic code points that have distinct uppercase forms are converted.

What happens to character array dimensions?

RunMat uppercases each row independently and pads with spaces when an uppercase mapping increases the row length. This mirrors MATLAB’s behaviour so the result always has rectangular dimensions.

Can I pass numeric arrays to upper?

No. Passing numeric, logical, or struct inputs raises a MATLAB-compatible error. Convert the data to a string or character array first (for example with string or char).

How are missing strings handled?

Missing string scalars remain <missing> and are returned unchanged. This matches MATLAB’s handling of missing values in text processing functions.

Will upper ever execute on the GPU?

Not today. The builtin gathers GPU-resident data automatically and performs the conversion on the CPU so the results match MATLAB exactly. Providers may add device-side kernels in the future, but behaviour will remain compatible.

See Also

lower, string, char, regexprep, strcmpi

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