Convert list of indices to array

Hello,

I have a 27x4 matrix with symbolic entries, say X, as seen below.

[ 1, 1, 1, 0]

[ 2, 1, 1, 0]

[ 3, 1, 1, e31]

[ 1, 2, 1, 0]

[ 2, 2, 1, 0]

[ 3, 2, 1, 0]

[ 1, 3, 1, e15]

[ 2, 3, 1, 0]

[ 3, 3, 1, 0]

[ 1, 1, 2, 0]

[ 2, 1, 2, 0]

[ 3, 1, 2, 0]

[ 1, 2, 2, 0]

[ 2, 2, 2, 0]

[ 3, 2, 2, e32]

[ 1, 3, 2, 0]

[ 2, 3, 2, e24]

[ 3, 3, 2, 0]

[ 1, 1, 3, e15]

[ 2, 1, 3, 0]

[ 3, 1, 3, 0]

[ 1, 2, 3, 0]

[ 2, 2, 3, e24]

[ 3, 2, 3, 0]

[ 1, 3, 3, 0]

[ 2, 3, 3, 0]

[ 3, 3, 3, e33]

From this, I would like to create a 3D array, say x, in which the columns are the index values that map to the fourth column in X. For example, once x is created, I would be able to make the call x(2,2,3) and it would return the symbolic 'e24'; calling x(2,1,1) returns 0; and so forth. Thank you for your help!

Answer 1

[Cris LaPierre]

You should be able to use the reshape command on the 4th column

% Setup your matrix
syms e31 e15 e32 e24 e33
a= [1, 1, 1,   0;
 2, 1, 1,   0;
 3, 1, 1, e31;
 1, 2, 1,   0;
 2, 2, 1,   0;
 3, 2, 1,   0;
 1, 3, 1, e15;
 2, 3, 1,   0;
 3, 3, 1,   0;
 1, 1, 2,   0;
 2, 1, 2,   0;
 3, 1, 2,   0;
 1, 2, 2,   0;
 2, 2, 2,   0;
 3, 2, 2, e32;
 1, 3, 2,   0;
 2, 3, 2, e24;
 3, 3, 2,   0;
 1, 1, 3, e15;
 2, 1, 3,   0;
 3, 1, 3,   0;
 1, 2, 3,   0;
 2, 2, 3, e24;
 3, 2, 3,   0;
 1, 3, 3,   0;
 2, 3, 3,   0;
 3, 3, 3, e33];

% reshape to a 3x3x3
x = reshape(a(:,4),3,3,3)

x(:,:,1) = 

x(:,:,2) = 

x(:,:,3) = 

x(2,2,3)

ans = 

x(2,1,1)

ans = 

0

[Christopher Kube]

Perfect! Thank you. I think this can easily be generalized as well with N being the dimension of the matrix.

x = reshape(a(:,end),ones(1,N)*3);

Answer 2

[David Hill]

x=reshape(yourMatrix(:,4),[3],[3],[3]);