join — Join text elements with delimiters in MATLAB and RunMat.

join(text, delimiter, dim) concatenates text along a chosen dimension and inserts delimiters between neighboring elements. Default dimension, delimiter broadcasting, and missing-string behavior follow MATLAB semantics.

Syntax

out = join(str)
out = join(str, delimiter)
out = join(str, dim)
out = join(str, delimiter, dim)
out = join(str, dim, delimiter)

Inputs

Returns

Errors

How join works

• When you omit the dimension, join operates along the last dimension whose size is not 1. If all dimensions are singleton, it uses dimension 2.
• The default delimiter is a single space character. You can pass a scalar delimiter (string or character vector) or supply a string/cell array whose shape matches the input, with the join dimension reduced by one, to customise delimiters for each gap.
• Inputs may be string scalars, string arrays (including N-D), character arrays, or cell arrays of character vectors. Cell inputs return cell arrays; all other inputs return string scalars or string arrays.
• If any element participating in a join is the string <missing>, the result for that slice is also <missing>, matching MATLAB’s missing propagation rules.
• Joining along a dimension greater than ndims(str) leaves the input unchanged.

Does RunMat run join on the GPU?

join executes on the CPU. When text or delimiters reside on the GPU, RunMat gathers them to host memory before performing the concatenation, ensuring identical results to MATLAB. Providers do not need to implement custom kernels for this builtin today.

GPU memory and residency

No. Text manipulation currently runs on the CPU. If your text or delimiters were produced on the GPU, RunMat gathers them automatically so that you can call join without extra steps.

Examples

Combine Strings In Each Row Of A Matrix

names = ["Carlos" "Sada"; "Ella" "Olsen"; "Diana" "Lee"];
fullNames = join(names)

Expected output:

fullNames = 3×1 string
    "Carlos Sada"
    "Ella Olsen"
    "Diana Lee"

Insert A Custom Delimiter Between Elements

labels = ["x" "y" "z"; "a" "b" "c"];
joined = join(labels, "-")

Expected output:

joined = 2×1 string
    "x-y-z"
    "a-b-c"

Provide A Delimiter Array That Varies Per Row

str = ["x" "y" "z"; "a" "b" "c"];
delims = [" + " " = "; " - " " = "];
equations = join(str, delims)

Expected output:

equations = 2×1 string
    "x + y = z"
    "a - b = c"

Join Along A Specific Dimension

scores = ["Alice" "Bob"; "92" "88"; "85" "90"];
byColumn = join(scores, 1)

Expected output:

byColumn = 1×2 string
    "Alice 92 85"    "Bob 88 90"

Join A Cell Array Of Character Vectors

C = {'GPU', 'Accelerate'; 'VM', 'Interpreter'};
result = join(C, ", ")

Expected output:

result = 2×1 cell
    {'GPU, Accelerate'}
    {'VM, Interpreter'}

Join Using A Dimension Argument As The Second Input

words = ["RunMat"; "Accelerate"; "Planner"];
sentence = join(words, 1)

Expected output:

sentence = "RunMat Accelerate Planner"

Join Rows Of An Empty String Array

emptyRows = strings(2, 0);
out = join(emptyRows)

Expected output:

out = 2×1 string
    ""
    ""

Using join with coding agents

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

FAQ

Related Strings functions

Open-source implementation

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

• View the source for join 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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