reshape a 2D to 3D matrix

Question

Yujiao Li 2015-3-31

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/195448-reshape-a-2d-to-3d-matrix

编辑： Star Strider 2015-3-31

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     2
   5     2
Matrix(:,:,2)=  
   2     4
   4     7
Matrix(:,:,3)=  
   2     4
   4     7
   5     11

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Answer 1

Star Strider 2015-3-31

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在 MATLAB Online 中打开

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]

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Yujiao Li 2015-3-31

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 2015-3-31

编辑：Star Strider 2015-3-31

在 MATLAB Online 中打开

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