how can I modify a triple "for" cycle to run faster?

Hi,

I have the following code, where I fill a 3D matrix with data from a struct, which has tables inside. The goal is to concatenate several 3D matrix. However, they have dfferent number of columns, so I don't think I can concatenate them all directly and skip the code below. The code below is taking me really a long time to compute, like days. My question is: how can I modify my code to make it run faster? I know I can preallocate B as B=zeros(50,10000,30), but I would like to know if there any other options. Thank you.

ntables=50
nlines=10000
ncolumns=30

for i=1:1:ntables
    for j=1:1:nlines
        for k=1:1:ncolumns
            B(i,j,k)=table2array(A((i)).data.A_data(j,k))
            
        end
    end
end

Answer 1

[Jan]

Of course you have to pre-allocate.

ntables  = 50;
nlines   = 10000;
ncolumns = 30;
B = zeros(ntables, nlines, ncolumns);
for i = 1:ntables
    B(i, :, :) = table2array(A(i).data.A_data(:, 1:ncolumns));
end