Call one array from a large array made up of several others

I've got an array, say Z, made up of 4 smaller 2x2 ones, say A, B, C and D:

Z = a11 a12 b11 b12
    a21 a22 b21 b22
    c11 c12 d11 d12
    c21 c22 d21 d22

Once I've created Z, is there a way to ask matlab for, for example, the first entry in each of A, B, C and D, based only on Z? I can call individual entries from it fine (e.g. the value at the 4th row, 3rd column), but would like to be able to store my data in one array and still treat it as individual arrays for some things.

Answer 1

[sixwwwwww]

you can do it fi you store your arrays A, B, C and D in cell array Z as follows:

Z = {A, B, C, D};

then you can treat A, B, C and D individually by using cell indexing

[Jennifer]

Hi - thanks for answering so quickly! I think I might not quite follow what you mean. I set up Z as you suggested, and now Z is shown as: [2x2 double] [2x2 double] [2x2 double] [2x2 double] I haven't been able to call an individual entry within the [2x2 double]s from this, is there a change in using cell indexing from treating an individual array?

[sixwwwwww]

here is the way you can do it:

% Your matrices A, B, C and D
A = ones(2); 
B = A;
C = A;
D = A;
% Cell array of your matrices
Z = {A, B, C, D};
% Now if you want to access A and want to replace its each element with 2 then you can do it as follow
Z{1}(:) = 2;
% Now if you want to access B and want replace its first element with 3 then you can do it as follow
Z{2}(1, 1) = 3;
% Now you can see the changes you made to A and B
disp(Z{1})
disp(Z{2})

In the same way you can easily you use matrices A, B, C and D by using proper cell indexing as described above

[Jennifer]

Thank you! I hadn't come across the disp(Z{1}) part before, it works now

Answer 2

[Matt J]

 Z([1,3],[1,3])

[Jennifer]

Hi - thanks for the quick answer! I haven't been able to get your suggestion to work, here's what I tried:

A = [1 2; 1 2];
B = [3 3; 4 4];
C = [9 8; 7 6];
D = [2 4; 6 8];
Z = {A B; C D}
Z([1,2],[1,2])

and that gives:

ans = 

      [2x2 double]    [2x2 double]
      [2x2 double]    [2x2 double]

Have I misunderstood a part of this?

[Matt J]

Here are some examples,

>> Z=10*reshape(1:16,4,4)'

Z =

      10    20    30    40
      50    60    70    80
      90   100   110   120
     130   140   150   160

>> Z([1,3],[1,3])

ans =

      10    30
      90   110

>> Z([2,4],[2,3])

ans =

      60    70
     140   150