gathering specific rows from each submatrices or cell arrays

Question

I hope to gather last lines from each submatrix or cell arrays.

• I have 17 x 20 cells in matrix name A.

• Each submatrices have different number of lines, but same number of columns (total 7 columns, all)

• I tried to generate a file, made up of only last rows of each submatrices. My target file's from will be

       M = [column1 column2 column3 column4 column5 column6 column7] 
       % made up of last rows of each submatrices, unknown number of lines, 7 columns
  

• So I tried

       for x_cc = 1:20
           for y_cc = 1:17
                M = A{x_cc, y_cc}(end,:);
           end
       end
  

• But it is not working, giving the error Subscript indices must either be real positive integers or logicals.

• Should I need to define the size first? What operation should be done? or what commands are useful? I tried cellfun, but not sure how can I use here.

• Need any help to solve this situation. Thanks~!

Answer 1

First off, it looks like you switched x_cc and y_cc. Since your matrix is 17 x 20, x_cc is the rows and should go to 17, while y_cc will go to 20.

However, the error you're getting is probably coming from trying to index an empty array (one of those contained in A) using end. An example of this error:

a = [];

a(end)
??? Subscript indices must either be real positive integers or logicals.

If you're curious, a method avoiding for loops would look like:

B = cellfun(@(x) x(end,:), A, 'UniformOutput', 0);  
M = cell2mat(B(:));

This grabs the last row from each matrix in A, then stacks them vertically and transforms to an array.