setdiff — Return values that appear in the first input but not the second, matching MATLAB ordering rules.

setdiff(A, B) returns the set of values (or rows) that appear in A but not in B. Results are unique, and the function can operate in sorted or stable order as well as row mode.

How setdiff works

• setdiff(A, B) flattens inputs column-major, removes duplicates, subtracts the values of B from A, and returns the remaining elements sorted ascending by default.
• [C, IA] = setdiff(A, B) also returns indices so that C = A(IA).
• setdiff(A, B, 'stable') preserves the first appearance order from A instead of sorting.
• setdiff(A, B, 'rows') treats each row as an element. Inputs must share the same number of columns.
• Character arrays, string arrays, logical arrays, numeric types, and complex values are all supported.
• Legacy flags ('legacy', 'R2012a') are not supported; RunMat always follows modern MATLAB semantics.

How RunMat runs setdiff on the GPU

setdiff is registered as a residency sink. When tensors reside on the GPU and the active provider does not yet implement a setdiff hook, RunMat gathers them to host memory, performs the CPU implementation, and materialises host-resident results. Future providers can wire a custom hook to perform the set difference directly on-device without affecting existing callers.

Examples

Finding values exclusive to the first numeric vector

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

Expected output:

C =
     5
IA =
     1

Preserving input order with 'stable'

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

Expected output:

C =
     2
IA =
     2

Working with rows of numeric matrices

A = [1 2; 3 4; 1 2];
B = [3 4; 5 6];
[C, IA] = setdiff(A, B, 'rows')

Expected output:

C =
     1     2
IA =
     1

Computing set difference for character data

A = ['m','z'; 'm','a'];
B = ['a','x'; 'm','a'];
[C, IA] = setdiff(A, B)

Expected output:

C =
    m
IA =
     1

Subtracting string arrays by row

A = ["alpha" "beta"; "gamma" "beta"];
B = ["gamma" "beta"; "delta" "beta"];
[C, IA] = setdiff(A, B, 'rows', 'stable')

Expected output:

C =
  1x2 string array
    "alpha"    "beta"
IA =
     1

Using setdiff with GPU arrays

G = gpuArray([10 4 6 4]);
H = gpuArray([6 4 2]);
C = setdiff(G, H)

Expected output:

C =
    10

FAQ

Related Array functions

Open-source implementation

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

• View setdiff.rs on GitHub
• Learn how the runtime works
• Found a bug? Open an issue with a minimal reproduction.

About RunMat

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