Dividing a Matrix into submatrices according to a specific column value

Question

Michail Isaakidis 2019-1-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/439192-dividing-a-matrix-into-submatrices-according-to-a-specific-column-value

评论： Michail Isaakidis 2019-1-11

Hi all!

So I have a very big matrix (10000x6 elements) with all my data and one of the columns contains the group that each set of data belongs (from 1 to 500). How would it be possible to seperate them with into individual matrices with the use of the group number?

Thank you in advance.

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Answer 1

rakbar 2019-1-10

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https://ww2.mathworks.cn/matlabcentral/answers/439192-dividing-a-matrix-into-submatrices-according-to-a-specific-column-value#answer_355923

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Use MATLAB findgroup and splitapply functions. Here is an example:

https://www.mathworks.com/help/matlab/ref/splitapply.html#bux2_9d

% create a random matrix 10 x 4
A = rand(10,4);
% the 5th column is the "Gourp" column
A(:,5) = [ 1 1 2 2 3 3 4 4 5 5 ];
% Find the "Grouping" vector
G = findgroups(A(:,5));
% function to return gourped sum matrix
func = @(x){(x)};
% return each submatrix (cell array)
Y = splitapply(func,A,G);

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Michail Isaakidis 2019-1-11

Thank you very much! That solved my problem!

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Answer 2

Akira Agata 2019-1-10

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https://ww2.mathworks.cn/matlabcentral/answers/439192-dividing-a-matrix-into-submatrices-according-to-a-specific-column-value#answer_355927

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The following is an another way that is easy to understand intuitively:

% create a random matrix 10 x 4
A = rand(10,4);
% the 5th column is the "Gourp" column
A(:,5) = [ 1 1 2 2 3 3 4 4 5 5 ];
% Find unique values
ID = unique(A(:,5));
% Separate the matrix
Y = cell(size(ID));
for kk = 1:numel(ID)
  idx = A(:,5) == ID(kk);
  Y{kk} = A(idx,:);
end