intersect — Return common elements or rows across arrays in MATLAB and RunMat.

intersect(A, B) computes the set intersection of A and B. Default ordering and optional index outputs follow MATLAB semantics.

Syntax

C = intersect(A, B)
C = intersect(A, B, option...)
[C, ia] = intersect(A, B)
[C, ia] = intersect(A, B, option...)
[C, ia, ib] = intersect(A, B)
[C, ia, ib] = intersect(A, B, option...)

Inputs

Returns

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

Errors

How intersect works

• intersect(A, B) flattens both inputs column-major, removes duplicates, and returns the sorted intersection.
• [C, IA, IB] = intersect(A, B) also returns index vectors so that C = A(IA) and C = B(IB).
• intersect(A, B, 'stable') preserves the first appearance order from A.
• intersect(A, B, 'rows') treats each row as an element. Inputs must share the same number of columns.
• Character arrays, string arrays, logical arrays, complex values, and numerical types are fully supported. Mixed classes raise a descriptive error.
• Legacy flags such as 'legacy' or 'R2012a' are not supported in RunMat.

Does RunMat run intersect on the GPU?

intersect registers as a residency sink. When the active acceleration provider offers a dedicated intersect hook, the set logic can execute directly on the device and return GPU-resident results. Until such a hook lands, RunMat automatically gathers GPU tensors to host memory, runs the CPU implementation, and materializes host-side outputs so behavior matches MathWorks MATLAB exactly.

GPU memory and residency

You usually do not need to call gpuArray manually. RunMat's planner keeps tensors resident on the GPU when profitable. If a provider lacks an intersect kernel the runtime gathers automatically, so explicit residency management is rarely needed. Explicit calls to gpuArray remain available for compatibility with MathWorks MATLAB workflows.

Examples

Finding common values in numeric vectors

A = [5 7 5 1];
B = [7 1 3];
[C, IA, IB] = intersect(A, B)

Expected output:

C =
     1
     7
IA =
     4
     2
IB =
     2
     1

Preserving input order with 'stable'

A = [4 2 4 1 3];
B = [3 4 5 1];
C = intersect(A, B, 'stable')

Expected output:

C =
     4
     1
     3

Intersecting matrix rows

A = [1 2; 3 4; 1 2];
B = [2 3; 1 2];
[C, IA, IB] = intersect(A, B, 'rows')

Expected output:

C =
     1     2
IA =
     1
IB =
     2

Working with strings and character arrays

names1 = ["apple" "orange" "pear"];
names2 = ["pear" "grape" "orange"];
[common, IA, IB] = intersect(names1, names2, 'stable')

Expected output:

common =
  1×2 string array
    "orange"    "pear"
IA =
     2
     3
IB =
     3
     1

Using intersect on GPU arrays

G = gpuArray([10 4 6 4]);
H = gpuArray([6 4 2]);
result = intersect(G, H)

Expected output:

result =
     4
     6

Using intersect with coding agents

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

FAQ

Related Array functions

Open-source implementation

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

• View the source for intersect 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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• RunMat automatically optimizes your math for GPU execution on Apple, Nvidia, and AMD hardware. No code changes needed. Simulations that took hours now take minutes.
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