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CategoryCells: Core

What does the cell2mat function do in MATLAB / RunMat?

cell2mat(C) concatenates the numeric, logical, complex, or character arrays stored in the cell array C into a single dense MATLAB array. The cell array must form a rectangular block structure: all cells in the same row share the same number of rows, all cells in the same column share the same number of columns, and higher-dimensional extents agree everywhere.

How does the cell2mat function behave in MATLAB / RunMat?

  • Works for cell arrays whose elements are numeric, logical, complex, or character arrays (including scalars and empties). Mixed types are rejected.
  • RunMat currently represents cell arrays as 2-D grids. The first dimension tiles rows, the second tiles columns, and any higher dimensions inside each element must agree exactly across all cells.
  • Empty cells contribute zero extent in their tiling dimension while preserving type information.
  • The output array uses column-major layout for numeric, logical, and complex data, and matches MATLAB character array semantics for text.
  • Calling cell2mat on an empty cell array returns the empty double matrix 0×0.

cell2mat Function GPU Execution Behaviour

cell2mat is inherently a host operation because MATLAB cell arrays live on the CPU heap. If a cell element is a GPU tensor (gpuArray) RunMat gathers it to host memory before concatenating. Providers do not need to implement bespoke kernels: the builtin terminates GPU fusion groups, materialises the inputs on the host, and returns a host-resident array.

GPU residency in RunMat (Do I need gpuArray?)

You usually do NOT need to call gpuArray before cell2mat. The builtin always gathers GPU-resident elements to the host so it can stitch the resulting matrix in CPU memory. Explicitly wrapping each cell in gpuArray is harmless, but there is no residency benefit because the final result is a standard CPU array.

Examples of using the cell2mat function in MATLAB / RunMat

Converting a 2-by-2 cell array of scalars into a matrix

C = {1, 2; 3, 4};
A = cell2mat(C);

Expected output:

A =
     1     2
     3     4

Concatenating blocks of different column widths

C = {[1 2], [3 4 5]; [6 7], [8 9 10]};
A = cell2mat(C);

Expected output:

A =
     1     2     3     4     5
     6     7     8     9    10

Converting logical cell contents into a logical matrix

C = {true(2,1), false(2,1)};
M = cell2mat(C);

Expected output:

M =
  2×2 logical array
     1     0
     1     0

Handling complex-valued blocks

C = {1+2i, [3+4i 5+6i]};
Z = cell2mat(C);

Expected output:

Z =
   1.0000 + 2.0000i   3.0000 + 4.0000i   5.0000 + 6.0000i

Producing character matrices from cell arrays of character rows

C = {'foo', 'bar'; 'baz', 'qux'};
S = cell2mat(C);

Expected output:

S =
    'foobar'
    'bazqux'

Tiling higher-dimensional numeric blocks

C = {ones(2,2,3), 2*ones(2,1,3)};
X = cell2mat(C);
size(X)

Expected output:

ans =
     2     3     3

Working with empty cells

C = {[], []; [], []};
A = cell2mat(C);
size(A)

Expected output:

ans =
     0     0

Gathering GPU tensors stored inside cells

G = gpuArray(ones(4,1));
C = {G, 2*G};
H = cell2mat(C);   % gathered back to host automatically
classUnderlying(H)

Expected output:

ans =
    'double'

FAQ

What element types does cell2mat support?

Numeric doubles (scalars or arrays), complex doubles, logical values, and character arrays. Mixed types are not allowed; every populated cell must have the same fundamental type.

Can I convert a cell array that contains structs or strings?

No. cell2mat requires array-like contents. Use specialised functions such as string or char converters for string data, or bespoke logic for structs and tables.

Do the cell contents need identical shapes?

Cells in the same row must share the same number of rows. Cells in the same column must share the same number of columns. Any higher dimensions must agree across all cells. Violations produce a descriptive error that mirrors MATLAB's behaviour.

What happens with empty cells?

Empty cells contribute zero extent along their tiling dimension. For example, if every element in a row is empty, the resulting matrix has zero rows for that block. Completely empty cell arrays produce the 0×0 empty double matrix.

Does cell2mat return GPU arrays when inputs are gpuArray elements?

Not yet. RunMat gathers GPU elements to the host before concatenating. Future releases may introduce GPU-resident cell storage, at which point providers can supply dedicated kernels.

See Also

cell, mat2cell, num2cell, cellfun

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