Convert list of indices to array

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Christopher Kube
Christopher Kube 2021-9-20
评论： Christopher Kube 2021-9-20
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!

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采纳的回答

Cris LaPierre
Cris LaPierre 2021-9-20
Ran in:
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
  1 个评论
Christopher Kube
Christopher Kube 2021-9-20
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);

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更多回答（1 个）

David Hill
David Hill 2021-9-20
x=reshape(yourMatrix(:,4),[3],[3],[3]);

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