hwo to arrange certain rows of a matrix into cell array

Hello!

I need to arrange certain rows of a matrix into a cell array. The data matrix is arranged as follows: [positionx positiony time ID] I would like to place in array{i} all the rows that share the same ID.

Anybody has an idea how to do that?

Thanks, Jack

Answer 1

[Azzi Abdelmalek]

A=[1 2 0 12;2 3 1 54;7 8 2 12;2 10 3 12;0 1 4 54;1 1  4 77]
[ii,jj,kk]=unique(A(:,4))
out=accumarray(kk,1:numel(kk),[],@(x) {A(x,:)})
celldisp(out)

[jack]

Thanks a lot! very brief script and it worked very well with my data.

Answer 2

[the cyclist]

Here's one way:

% Some pretend data
data = [1 2 3 1; ...
        4 5 6 2; ...
        7 8 9 1];

% Identify the unique IDs, and indices to them
[uniqueId,~,indexFromUniqueBackToAll] = unique(data(:,4));

% Convenient to define the number of unique ids
numberUniqueIds = numel(uniqueId);

% Preallocate memory for the cell array
cellData = cell(numberUniqueIds,1);

% For each unique id, fill in the cell array
for nu = 1:numberUniqueIds
    indexToThisId = (indexFromUniqueBackToAll==nu);
    cellData{nu} = data(indexToThisId,:); 
end

[jack]

Thank you very much!