reshape a 2D to 3D matrix

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Yujiao Li
Yujiao Li on 31 Mar 2015
Edited: Star Strider on 31 Mar 2015
My data
ID X1 X2
1 1 2
1 5 2
2 2 4
2 4 7
3 2 4
3 4 7
3 5 11
My goal is to have the submatrix based on the ID. The question is when the rows of each submatrix is not the same, how can i get the following result?
Matrix(:,:,1)=
1 1 2
1 5 2
Matrix(:,:,2)=
2 2 4
2 4 7
Matrix(:,:,3)=
3 2 4
3 4 7
3 5 11

Answers (1)

Star Strider
Star Strider on 31 Mar 2015
You have to use a cell array, but it is relatively easy:
D = {1 1 2
1 5 2
2 2 4
2 4 7
3 2 4
3 4 7
3 5 11};
Matrix = {D(1:2,:) D(3:4,:) D(5:7,:)};
Matrix{:} % Check Result
produces:
ans =
[1] [1] [2]
[1] [5] [2]
ans =
[2] [2] [4]
[2] [4] [7]
ans =
[3] [2] [ 4]
[3] [4] [ 7]
[3] [5] [11]
  3 Comments
Yujiao Li
Yujiao Li on 31 Mar 2015
Thanks a lot. But my goal is to construct a 3D data stucture by loop. so that I can use x(:,:,i) and x(:,:,j) to calculate further. Could you help me on improve my code:
ID.uni=unique(ID); k=length(ID.uni); X=[]; for i=1:k rows_i= D(:,1)==ID.uni(i); % index which rows have the same ID X(:,:,i)=D(rows_i,2:3); end
Thank you so much!
Star Strider
Star Strider on 31 Mar 2015
Edited: Star Strider on 31 Mar 2015
My pleasure!
It has to be a cell array, so I would simply do this, taking advantage of the third output of unique, using accumarray as a bin counter, and mat2cell to create the cell array:
D = [1 1 2
1 5 2
2 2 4
2 4 7
3 2 4
3 4 7
3 5 11];
[IDuni,~,ic]=unique(D(:,1));
rows_i = accumarray(ic,1);
X = mat2cell(D, rows_i, 3)
Matrix_1 = X{1} % Display Resultd
Matrix_2 = X{2}
Matrix_3 = X{3}
producing:
X =
[2x3 double]
[2x3 double]
[3x3 double]
Matrix_1 =
1 1 2
1 5 2
Matrix_2 =
2 2 4
2 4 7
Matrix_3 =
3 2 4
3 4 7
3 5 11

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