Create a 4D array from 3D data set and a 2D variable location index

Hello, I am having some problems getting my head around creating a 4D array, and would appreciate some help with the fine tuning!

I have a set of 36 data sets, each of which is a 250 x 2 array. These comprise 12 readings, each repeated twice (so there are 3 sets of each reading which I will use to calculate a mean). These data sets are stored in data which is a 250 x 2 x 36 variable. I also have a matrix A which gives the location index of each 250 x 2 data set when I read them all in using a combination of files=dir() and dlmread(files.name). A looks like this:

A = [2 8 3 9 4 10 5 11 6 12 7 1; 
    14 20 15 21 16 22 17 23 18 24 19 13 ;
    26 32 27 33 28 34 29 35 30 36 31 25];

I would like to create a 4D matrix out of my 2D data sets by having a 3rd dimension which is the 12 different readings, and a 4th dimension which is the 3 incidences of each set.

So far I have used the cat() function in this way:

set= cat(4, data(:,:,A(1,:)), data(:,:,A(2,:)), data(:,:,A(3,:)));

I am sure though that there must be a more elegant way to do this without manually typing out 'data(:,:,A(1,:))' etc as this would not work if I had many more repeats.

Is there a better way for me to do this? I thought set= cat(4, data(:,:,A)) might work, but it takes A as a 1D list rather than a 2D matrix.

Thank you for your time!

[Azzi Abdelmalek]

I think you can make your question more clear if you post a simple and short example, and avoid describing things that will not help.

[ML]

Ok thanks for your feedback, here's another go at posing the question:

I have a 3D array a x b x c (called readings). c is a linear index of data a x b. I would like to change the linear index to a 2D array index d x e (called A) to group the data in a more meaningful way, thereby creating a 4D array. I can do this using

cat(4, readings(:,:,A(1,:)), readings(:,:,A(2,:)), readings(:,:,A(3,:)))

but I would like to know if there is a better way of doing this without specifying each of the rows of A individually or using a for loop.

Thanks!

Answer 1

[Matt J]

Looks like you could just do

      [m,n]=size(A);
      [p,q]=size(readings);

      A=A.';

      set=readings(:,:,A(:));

      set=reshape(set,p,q,n,[]);

[ML]

Thank you, that works perfectly.