Convert cell array of cell arrays to matrix of matrices

Question

I can convert a cell array of matrices to matrix:

>> C={[1,1]; [2,2]; [3,3]};
>> cell2mat(C)
ans =
     1     1
     2     2
     3     3
         


        

Answer 1

This should do the trick:

cellOfCells = {{1,1}; {2,2}; {3,3}};
cell2mat(cellfun(@cell2mat, cellOfCells, 'UniformOutput', false))

Edit:

I agree that keeping it simple is an important, but so is having fun :) So - here's a one-liner that should do the trick (and can be easily generalized for any size):

a = {{1,1;1,1}; {2,2;2,2}; {3,3;3,3}}
reshape(cell2mat(cellfun(@cell2mat,a, 'UniformOutput', false))', 2, 2, 3)

Answer 2

To be honest, I never liked cell2mat for being slow, so I've come up an alternative solution using comma-separated lists instead!

Transform a cell array of vectors

This is fairly simple, just use the colon operator and concatenate all vectors vertically:

C = {[1,1]; [2,2]; [3,3]};
A = vertcat(C{:})

and so we get:

A =
    1   1
    2   2
    3   3

Transform a cell array of cell arrays

This is a bit trickier. Since it's a cell array of cell arrays, we'll have to obtain a vector of all elements by a double use of the colon and horzcat, and then reshape it into the desired matrix.

C = {{1,1}; {2,2}; {3,3}};
V = [size(C{1}), 1]; V(find(V == 1, 1)) = numel(C);
A = reshape([horzcat(C{:}){:}], V)

and so we get:

A =
    1   1
    2   2
    3   3

The manipulation of V makes sure that A is reshaped correctly without having to specify the output dimensions explicitly (unfortunately, I didn't find a one liner for this). This also works for multi-dimensional cell arrays as well:

C = {{1, 1; 1, 1}; {2, 2; 2, 2}; {3, 3; 3, 3}};
V = [size(C{1}), 1]; V(find(V == 1, 1)) = numel(C);
A = reshape([horzcat(C{:}){:}], V)

A(:,:,1) = 
    1   1
    1   1

A(:,:,2) =   
    2   2
    2   2

A(:,:,3) =    
    3   3
    3   3

P.S

I think the correct result for the last example should be a 6-by-2 matrix instead of a 2-by-2-by-3. However, that is not what you requested, so it's off-topic.

Answer 3

I had the same error, I just commented out the lines in cell2mat that return the error and everything work fine to me.

lines to comment out in cell2mat (51:53): (you can find them using dbstop if error)

if cisobj || ciscell error(message('MATLAB:cell2mat:UnsupportedCellContent')); end

I don´t think it is a good idea to change matlab functions, and I am pretty shameful of my solution myself, but it works.

Answer 4

Okay, the question is a long time ago - but maybe my answer might help other readers or searchers.
I think the best solution is nearly the idea presented by Eitan T but it is possible to do that without reshaping. For me

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

does what was asked for - thus answers with

A(:,:,1) =
     1     1
     1     1
A(:,:,2) =
     2     2
     2     2
A(:,:,3) =
     3     3
     3     3

Hoping that helps.

Answer 5

keep it simple

c = {{1,1;1,1}; {2,2;2,2}; {3,3;3,3}};
z = zeros([size(c{1}) size(c,1)]);

for i=1:size(c,1)
    z(:,:,i)=cell2mat(c{i});
end

gives

EDU>> z    
z(:,:,1) =

     1     1
     1     1

z(:,:,2) =

     2     2
     2     2    

z(:,:,3) =

     3     3
     3     3