Merge multiple matrices with different columns into a single matrix

I would like to combine several matrices with different columns (cell_test(:,1)) into one matrix by adding 0's (or rather []) in the missing values (see 'M' matrix).

cell_test = importdata("cell_test.mat");   %first column: matrices; second column: number of columns in the matrix

col = cell_test(1:3,2);
col = cell2mat(col);
col_max = max(col);

null_A = repmat(0,2,col_max-cell_test{1,2});
null_C = repmat(0,2,col_max-cell_test{3,2});

A_new = [cell_test{1,1} , null_A];
C_new = [cell_test{3,1} , null_C];

M = [A_new; cell_test{2,1}; C_new];  % result (where 0 become '[]' (possible?))

I would try to get the matrix 'M' as generically as possible, i.e. that I want to get that result even if I have multiple rows within 'cell_test'.

Answer 1

[Voss]

load cell_test

One way:

% get the size of each matrix in cell_test(:,1)
sz = cellfun(@size,cell_test(:,1),'UniformOutput',false);
sz = vertcat(sz{:});

% max number of columns:
col_max = max(sz(:,2));

% function that appends columns of zeros (to fill to col_max)
% to a matrix m of size s:
f = @(m,s)[m zeros(s(1),col_max-s(2))];

% apply that function to each matrix in cell_test(:,1)
% and store the results in cell array C:
C = cellfun(f,cell_test(:,1),num2cell(sz,2), ...
    'UniformOutput',false);

% vertically concatenate all matrices in C together:
M = vertcat(C{:})

M = 6×5

173 326 327 0 0 3 1350 1351 0 0 175 332 333 334 335 9 1356 1357 1358 1359 176 335 336 337 0 11 1359 1360 1361 0

Another way:

% get the size of each matrix in cell_test(:,1)
sz = cellfun(@size,cell_test(:,1),'UniformOutput',false);
sz = vertcat(sz{:});

% keep track of row offsets, for where to assign each matrix into the
% result matrix:
rows = cumsum([1; sz(:,1)]);

% initialize result matrix:
M = zeros(rows(end)-1,col_max);

% loop over cell_test(:,1) and put each matrix in place in the result
% matrix:
for ii = 1:size(cell_test,1)
    M(rows(ii):rows(ii+1)-1,1:sz(ii,2)) = cell_test{ii,1};
end

% show the result:
disp(M);

         173         326         327           0           0
           3        1350        1351           0           0
         175         332         333         334         335
           9        1356        1357        1358        1359
         176         335         336         337           0
          11        1359        1360        1361           0