matrix indexing and creating a new matrix with new size

Dear experts, I hope somebody can help me. I have a n*4 matrix. In a loop I want to index some rows (the range is not fixed) from column 1 and put them in a new matrix with separate columns. I guess since the size of rows are not the same, Matlab gives me the mismatch dimension error for new matrix! Any solution? Thanks in advance Sobhan

Answer 1

[Wayne King]

How about

   clear output
   For f = 1:nfiles 
   IndexStart= RHs(RHs<peak); 
   IndexEnd= RHs(RHs>peak); 
   output{f} = Mydata (Index1:Index2,1); 
   end

If you know how big output is going to be in advance you can preallocate the cell array.

[Sobhan]

thanks Wayne,

your solution only gives me a cell array with the size of output and not a matrix.

Cheers

Answer 2

[Wayne King]

How about using a cell array? Beyond that I think you will need to give us a little MATLAB example to illustrate your issue.

[Sobhan]

Hi Wayne,

This is a simplified version of my loop.

For f = 1:nfiles

IndexStart= RHs(RHs<peak);

IndexEnd= RHs(RHs>peak);

output (:, f) = Mydata (Index1:Index2,1);

End

only the first file can be saved in output but it gives error for the second file because it has different rows. Is it clear now? Sorry I am really new to matlab.

Cheers

Sobahn

Answer 3

[Christoph]

Hi Sobhan,

as Wayne said, an example might be helpful. Nevertheless you might use:

X_new(:,end+1) = [X_old(:,i); zeros(size(X_new, 1) - size(X_old, 1),1)];

in your loop as long as the length of the old matrix is shorter or equal as the length of the new one. But waynes answer is the "politcally correct" one.

[Sobhan]

Hi,

Thanks for the answer. I gave an example above.

The length of the new matrix is sometimes bigger sometimes smaller. I think I need something to add a new column with the size of new file to previously created matrix. I am trying to figure it out.

Cheers

[Christoph]

ok, try to implement the next few nasty codelines:

if length(X_new) < length(X_old)

X_new(end+1,:) = zeros(length(X_old)-length(X_new), size(X_new, 2))

end

Answer 4

[Sobhan]

Cell array was the solution: output{f} = Mydata (Index1:Index2,1)