Loop multidimensional array doesn't work

Let's say I have some data TxN. The first column (N_1) of the data changes every time, while the rest stays fixed. Therefore, I want to create a multidimensional array TxNxM, where M takes care of the different N_1s.

Let me take an example to make it clearer:

% original data where x changes every time while z is always the same

x = randn(100,10);
z = ones(100, 5);

% this is just one of the 10 datasets
y = [x(:,1),z];

% store results
Y = nan(size(y,1), size(y,2),size(x,2));

% Create 10 datasets where the first column changes every time (x(:,i))
% while the rest stays fixed

for i = size(x,2)
    Y(:,:,i) = [x(:,i), z];
end

The issue with this is that I only get data for the last column of x while all the rest is NaN.

What am I doing wrong?

Can anyone help me?

Answer 1

[Matt J]

You could fix it by changing the opening of your for-loop to,

for i = 1:size(x,2)

but below is a more efficient loop-free method.

Y = nan(size(y,1), size(y,2),size(x,2));

Y(:,1,:)=x;
Y(:,2:end,:)=repmat(z,1,1,size(x,2));

[Armando MAROZZI]

thanks a lot!

[Matt J]

I would like to note, though, that it seems a bit wasteful to put so much duplicate data in Y. I don't see why working with x and z as separate arrays wouldn't be preferred.

[Armando MAROZZI]

I see your points. However, I need to apply a function to different datasets (of the same type you saw above) and that's the quickest solution I came up with