Storing each iteration of a loop in Matlab

Question

I have a 2d matrix (A=80,42), I am trying to split it into (80,1) 42 times and save it with a different name. ie

M_n1 , M_n2 , M_n3 , … etc (representing the number of column)

I tried

for i= 1:42
    M_n(i)=A(:,i)
end

it didn't work

How can I do that without overwrite the result and save each iteration in a file (.txt) ?

Answer 1

You can use eval

for ii = 1:size(A,2)
    eval( sprintf( 'M_n%d = A(:,%d);', ii, ii ) );
    % now you have M_n? var for you to process
end

However, the use of eval is not recommanded , you might be better off using cell array

M_n = mat2cell( A, [size(A,1)], ones( 1, size(A,2) ) );

Now you have M_n a cell array with 42 cells one for each column of A .
You can access the ii -th column by M_n{ii}

Answer 2

Generally, doing if you consider doing this kind of things: don't. It does not scale up well, and having them in one array is usually far more convenient.

As long as the results have the same shape, you can use a standard array, if not you can put each result in a cell array eg. :

results = cell(nTests,1)
result{1} = runTest(inputs{1})

or even

results = cellfun(@runTest,inputs,'UniformOutput',false); % where inputs is a cell array

And so on.

If you do want to write the numbers to a file at each iteration, you could do it without the names with csvwrite or the like (since you're only talking about 80 numbers a time).

Another option is using matfile , which lets you write directly to a variable in a .mat file. Consult help matfile for the specifics.