Concatenate elements of cell arrays vertically

Hi I have a 3x1 cell array, where each cell contains a 2x8 double matrix:

A = {[8 9 0 0 1 0 1 0; 5 3 0 0 1 1 1 1];
    [2 4 0 0 0 0 1 0; 3 9 0 1 0 0 0 1];
    [6 2 1 1 1 0 1 1; 9 7 1 1 0 0 0 0]};

I would like to concatenate vertically the first matrix's rows in each cell and get this 3x8 double matrix:

B =
     8     9     0     0     1     0     1     0
     2     4     0     0     0     0     1     0
     6     2     1     1     1     0     1     1

I tried something like

vertcat(A{:}(1,:))

but it did not work obviously.

Any simple idea without any loop for?

[Sim]

P.S.: with the loop for it would be:

for i = 1 : size(A,1)
    b(i,:) = A{i}(1,:);
end
B = vertcat(b)

[Stephen23]

B = vertcat(b) % <- does nothing

Preallocated b followed by a FOR loop is probably the most efficient approach.

[Sim]

Many thanks @Stephen for your suggestion !

Yes, sorry, this works:

for i = 1 : size(A,1)
    b{i} = A{i}(1,:);
end
B = vertcat(b{:});

Answer 1

[KSSV]

A = {[8 9 0 0 1 0 1 0; 5 3 0 0 1 1 1 1];
    [2 4 0 0 0 0 1 0; 3 9 0 1 0 0 0 1];
    [6 2 1 1 1 0 1 1; 9 7 1 1 0 0 0 0]};
iwant = cell2mat(cellfun(@(x) x(1,:),A,'UniformOutput',false))

iwant = 3×8

8 9 0 0 1 0 1 0 2 4 0 0 0 0 1 0 6 2 1 1 1 0 1 1

Note that cellfun uses loop inside.

[Sim]

Thanks a lot @KSSV!

This solution works well for me :)

However, I have noticed that this solution is slightly slower then the traditional loop for.... strange :)

tic
iwant = cell2mat(cellfun(@(x) x(1,:),A,'UniformOutput',false));
toc

tic
for i = 1 : size(A,1)
    b{i} = A{i}(1,:);
end
iwant = vertcat(b{:});
toc

% solution with cellfun
Elapsed time is 0.000518 seconds.
% solution with the traditional loop for
Elapsed time is 0.000197 seconds.

Also for my case, which is bigger than A, the traditional loop for is faster...

% solution with cellfun
Elapsed time is 0.012030 seconds.
% solution with the traditional loop for
Elapsed time is 0.005301 seconds.

[KSSV]

Yes you are right. cellfun would be slow comapred to loop.