sort — Sort array elements along a dimension with MATLAB-compatible direction options and optional index outputs.

sort orders elements along a selected dimension, defaulting to ascending order on the first non-singleton dimension. It also supports MATLAB-compatible index outputs that return permutation positions.

Syntax

B = sort(A)
B = sort(A, arg1)
B = sort(A, arg1, arg2)
B = sort(A, ..., "ComparisonMethod", method)
B = sort(A, ..., "MissingPlacement", placement)
[B, I] = sort(A)

B = sort(A)
B = sort(A, arg1)
B = sort(A, arg1, arg2)
B = sort(A, ..., "ComparisonMethod", method)
B = sort(A, ..., "MissingPlacement", placement)
[B, I] = sort(A)
[B, I] = sort(A, arg1)
[B, I] = sort(A, arg1, arg2)
[B, I] = sort(A, ..., "ComparisonMethod", method)
[B, I] = sort(A, ..., "MissingPlacement", placement)

Inputs

Returns

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

Errors

How sort works

• Scalars remain unchanged; vectors are reordered into ascending or descending order.
• For matrices and higher-dimensional tensors, the sort operates along a specified dimension (default: first non-singleton). All other dimensions remain untouched.
• [B, I] = sort(A, ...) returns both the sorted values B and the permutation indices I, using MATLAB's one-based indexing.
• Direction arguments accept 'ascend' (default) or 'descend'.
• Name-value pairs support 'ComparisonMethod' with values 'auto', 'real', or 'abs'. The 'abs' option sorts by absolute value while breaking ties using the signed value.
• For complex inputs, the default 'ComparisonMethod'='auto' behaves like 'abs' (magnitude ordering) and 'real' compares the real component first with the imaginary component used for tie-breaking.
• NaN values are treated as missing: they appear at the end for ascending sorts and at the beginning for descending sorts (matching MATLAB's 'MissingPlacement','auto' behaviour for doubles).
• Dimensions greater than ndims(A) are treated as singleton dimensions (size 1) and therefore leave A unchanged while returning index values of 1.

Does RunMat run sort on the GPU?

sort is registered as a sink builtin. When tensors reside on a GPU without a specialised sort kernel, RunMat gathers them to host memory, performs the sort, and returns host-resident outputs.

Providers may implement a future sort_dim hook to keep data on the GPU. Until then, all providers fall back to the host path automatically.

The returned index tensor is always host-resident double precision.

Examples

Sorting a column vector in ascending order

A = [3; 1; 2];
B = sort(A)

Expected output:

B =
     1
     2
     3

Sorting rows by specifying the dimension

A = [1 4 2; 3 2 5];
B = sort(A, 2)

Expected output:

B =
     1     2     4
     2     3     5

Sorting values in descending order

A = [10 4 7 9];
B = sort(A, 'descend')

Expected output:

B =
    10     9     7     4

Retrieving permutation indices alongside the sorted values

A = [4 1 9 2];
[B, I] = sort(A)

Expected output:

B =
     1     2     4     9
I =
     2     4     1     3

Sorting by absolute value using ComparisonMethod

A = [-8 -1 3 -2];
B = sort(A, 'ComparisonMethod', 'abs')

Expected output:

B =
    -1    -2     3    -8

Sorting tensors containing NaN values

A = [NaN 4 1 2];
[B, I] = sort(A)

Expected output:

B =
     1     2     4   NaN
I =
     3     4     2     1

Sorting GPU tensors with automatic host fallback

G = gpuArray(randn(5, 1));
[B, I] = sort(G, 'descend')

Using sort with coding agents

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

FAQ

Related Array functions

Open-source implementation

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

• View the source for sort in Rust on GitHub
• Learn how the RunMat runtime works
• Found a bug? Open an issue with a minimal reproduction.

About RunMat

RunMat is an open-source runtime that executes MATLAB-syntax code blazing on any GPU. It is licensed under the Apache 2.0 license.

• 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.
• Start running code in seconds. RunMat runs in the browser, on the desktop, or from the CLI. No license server, no IT ticket.

Getting started · Benchmarks · Pricing