How does mat2cell work?

Question

Diego Hens 2021-1-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/717840-how-does-mat2cell-work

评论： Diego Hens 2021-1-15

采纳的回答： Steven Lord

Hello,

I need your help understanding how cell2mat works. I have tried so hard, but I just don't get it.

I have:

a Matrix called Matrix_A with a size of 18x46092.

I would like to:

separate it so, that I get 15364 cells (this is the amount of points, 46092/3, for the x, y and z coordinates), each of these cells containing a 18x3 matrix (18 points each).

I have already done it with a line someone gave me. It is for the mean of Matrix_A. It works.

Matrix_A  = transpose(mat2cell(mean(cell2mat(Matrix_A)), 1, 3*ones(size(Matrix_A,2),1)));

Can someone please explain how cell2mat works, so that I can use it myself? A solution (a line of code) solves the problem right now, but this is the second or third time I want to do this and can't. That's why I would prefere an easy to understand explanaition.

Thank you!

Edit: I cannot post the Matrix_A data as it is too big.

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Answer 1

Steven Lord 2021-1-15

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https://ww2.mathworks.cn/matlabcentral/answers/717840-how-does-mat2cell-work#answer_598815

Let's try this with a slightly smaller matrix, so you can see what's going on.

A = reshape(1:24, [3 8])
A = 3×8
     1     4     7    10    13    16    19    22
     2     5     8    11    14    17    20    23
     3     6     9    12    15    18    21    24

Let's slice this into 3-by-2 chunks. We don't actually need to slice it row-wise (since we want each chunk to have 3 rows just like A has three rows) but we do need to slice it column-wise.

rowSliceSizes = 3; % Each cell has three rows like A does
columnSliceSizes = [2 2 2 2]; % Each cell contains 2 columns of A

Now slice.

C = mat2cell(A, rowSliceSizes, columnSliceSizes)
C = 1x4 cell array
    {3×2 double}    {3×2 double}    {3×2 double}    {3×2 double}
celldisp(C)
 
C{1} =
 
     1     4
     2     5
     3     6

C{2} =
 
     7    10
     8    11
     9    12

C{3} =
 
    13    16
    14    17
    15    18

C{4} =
 
    19    22
    20    23
    21    24

Now let's slice A into a 2-by-3 cell array. Each cell in the first row of the result should contain 2 rows of A and each cell in the second row should contain the third row of A. Each cell in a column of the result contains 3, 2, and 3 columns of A respectively:

D = mat2cell(A, [2 1], [3 2 3])
D = 2x3 cell array
    {2×3 double}    {2×2 double}    {2×3 double}
    {1×3 double}    {1×2 double}    {1×3 double}
celldisp(D)
 
D{1,1} =
 
     1     4     7
     2     5     8

D{2,1} =
 
     3     6     9

D{1,2} =
 
    10    13
    11    14

D{2,2} =
 
    12    15

D{1,3} =
 
    16    19    22
    17    20    23

D{2,3} =
 
    18    21    24