Dividing a Matrix into submatrices according to a specific column value

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.

Answer 1

[rakbar]

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);

[Michail Isaakidis]

Thank you very much! That solved my problem!

Answer 2

[Akira Agata]

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