startsWith — Test whether text values start with specified prefixes using MATLAB-compatible broadcasting and case options.

startsWith(str, pattern) returns logical results indicating whether each text element begins with a corresponding prefix. It supports MATLAB-compatible string, char, and cellstr containers plus implicit expansion rules.

Syntax

tf = startsWith(str, pat)
tf = startsWith(str, pat, ignoreCase)
tf = startsWith(str, pat, "IgnoreCase", value)
tf = startsWith(str, pat, nameValuePairs...)

Inputs

Returns

Errors

How startsWith works

• Accepts text inputs as string scalars/arrays, character vectors/arrays, or cell arrays of character vectors.
• Accepts patterns in the same formats; scalar inputs expand across the other argument following MATLAB broadcast rules.
• Missing strings (<missing>) never match any pattern.
• Empty patterns ("" or '') always match non-missing text elements.
• Patterns that are <missing> never match and therefore return false.
• Character arrays treat each row as an independent element; zero-row character arrays yield empty outputs.
• The optional IgnoreCase flag can be supplied either as a trailing scalar or via the 'IgnoreCase', value name-value pair. It accepts logical/numeric scalars and the strings 'on', 'off', 'true', and 'false' (default is case-sensitive).
• Returns a logical scalar when the broadcasted size is one element, otherwise returns a logical array.

Does RunMat run startsWith on the GPU?

startsWith performs host-side prefix comparison. When inputs currently live on the GPU, RunMat gathers them back to the host before evaluation so the behaviour is identical to MATLAB. No acceleration provider hooks are required for this builtin.

GPU memory and residency

You usually do NOT need to call gpuArray yourself in RunMat (unlike MATLAB).

startsWith always executes on the host, but RunMat's runtime automatically gathers any GPU-resident inputs before evaluating the prefix check. Because the builtin registers a ResidencyPolicy::GatherImmediately, the planner gathers device handles eagerly and computes the logical result on the CPU. You may still call gpuArray manually for compatibility with MATLAB code; the runtime gathers the inputs just in time, so results match MATLAB precisely.

Examples

Determine whether a string starts with a prefix

tf = startsWith("RunMat Accelerate", "RunMat")

Expected output:

tf = logical
   1

Perform a case-insensitive prefix check

tf = startsWith("RunMat", "run", 'IgnoreCase', true)

Expected output:

tf = logical
   1

Ignore case using the legacy logical flag

tf = startsWith("RUNMAT", "run", true)

Expected output:

tf = logical
   1

Apply a scalar prefix to every element of a string array

labels = ["alpha" "beta" "gamma"];
tf = startsWith(labels, "a")

Expected output:

tf = 1×3 logical array
   1   0   0

Match element-wise prefixes with implicit expansion

names = ["hydrogen"; "helium"; "lithium"];
prefixes = ["hyd"; "hel"; "lit"];
tf = startsWith(names, prefixes)

Expected output:

tf = 3×1 logical array
   1
   1
   1

Test prefixes for a cell array of character vectors

C = {'Mercury', 'Venus', 'Mars'};
tf = startsWith(C, 'M')

Expected output:

tf = 1×3 logical array
   1   0   1

Provide multiple prefixes as a column vector

tf = startsWith("saturn", ['s'; 'n'; 'x'])

Expected output:

tf = 3×1 logical array
   1
   0
   0

Handle empty and missing values

texts = ["", "<missing>"];
tf = startsWith(texts, "")

Expected output:

tf = 1×2 logical array
   1   0

Using startsWith with coding agents

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

FAQ

Related Strings functions

Open-source implementation

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

• View the source for startsWith 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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