Is there a way to combine number of matrices into one?

Hi there, I would like to ask is there a way to join multiple matrices into a single one in a better way?

I was thinking maybe a for loop could do the job, but I don't know where to start as each data contains a different name.

For Example: Suppose I have 10 matrices, it is in the workspace as various name but equal sizes.

e.g) for all matrices in 10x10 size

matrix1_10

matrix11_20

matrix21_30.....

matrix91_100

I would like to join them into a column, so like 100x10 size matrix

I do know there is a way to do this.

If I would like to join each other vertically, well I could do [matrix1_10; matrix11_20 ; matrix21_30 ; ...... ; matrix91_100], it will do just fine.

However if the number of data was not 10 matrices, could be 1000, 10000 or more, what should I do in order to get the job done?

Like I said, probably a for loop may help me on this case. But I don't know what to begin with? Or is there a better solution to this?

Thank you.

Answer 1

[Jan]

If you have 1000 arrays, it would be a really bad idea to store them in different variables, e.g. by hinding an index in the name of the variable. See TUTORIAL: Why and how to avoid Eval

If you use a cell array instead, the solution is trivial:

matrix = cell(1, 10);
for k = 1:10
    matrix = cell(10, 10);
end
% Join the matrices vertically:
result = cat(1, matrix{:})

[Moses Tang]

Thank you very much! I will consider this method and give it a try.

Answer 2

[Stephan]

Hi,

this solution is evil - since it uses eval:

A = whos; 
A = {A.name};
B = string(ones(1,2*numel(A)-1));
B(2:2:end) = ",";
for k = 1:numel(A)
    B(2*k-1) = A{k};
end
M = eval(join(['vertcat(',B,')']));

To use it make sure that only your variables are in workspace you want to join!

Example:

clear
M1 = zeros(3)
M2 = ones(3)
M3 = M1
M4 = randi(10,3)

results in

M1 =

     0     0     0
     0     0     0
     0     0     0


M2 =

     1     1     1
     1     1     1
     1     1     1


M3 =

     0     0     0
     0     0     0
     0     0     0


M4 =

    10     4     5
     2     1    10
     3     7     5

After running the script:

>> M

M =

     0     0     0
     0     0     0
     0     0     0
     1     1     1
     1     1     1
     1     1     1
     0     0     0
     0     0     0
     0     0     0
    10     4     5
     2     1    10
     3     7     5

But note that this is bad style - read here:

https://de.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

Best regards

Stephan

[Moses Tang]

Although it's not the prefered method in joining the matrices, but thank you very much for your hardwork.

Thank you!