MATLAB: How to create a Nx3 array from Nx4 array

cell array convert

Hi all,

If I have a 100×1 cell array which contains 100 Nx4 double array where N is a variable size, how to I create a new cell array which is also 100×1, but contains a Nx3 double array that contains just columns 2,3 and 4 of the previous Nx4 array?

Hope that make sense! I'd appreciate any help with this problem.

Thanks in advance!

Best Answer

You can use cellfun()

C1; % 100x1 with Nx4 matrices
C2 = cellfun(@(x) {x(:,2:end)}, C1);

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MATLAB: Split the 132×10 cells into 1×10 arrays

nx = 1320 ; ny = 10 ;
%%Make a random data
A = cell(nx,ny) ;
for i = 1:nx
    for j = 1:ny
        A{i,j} = rand ;
    end
end
%%split into 1x10 cell arrays 
iwant = cell(nx,1) ;
for i = 1:nx
    iwant{i,:} = [A{i,:}] ;
end

MATLAB: Search nx3 array row-wise for 2 equal elements

My initial idea is below, but someone may be able to improve on it in efficiency or elegance.

There is an awkwardness in this solution: if row A has two elements in common with both rows B and C, then the results may contain both [A B C] and [B C]. There are various things you could do about this - but a more precise specification of the problem is needed in order to choose how to handle such cases. If the data only ever has pairs of matching rows, there's no problem.

% data
a = [5 6 2;
 3 2 7;
 4 6 5;
 9 7 2;
 5 3 8]
% code
ap = a.';
groups = cell(1, size(ap,2)-1); % pre-allocate cell array for results
ngroups = 0;
for k = 1:size(ap, 2)-1    % loop over rows of a (cols of ap)
    same = bsxfun(@ismember, ap(:,k), ap(:,k+1:end));  % find common elements
    matches = find(sum(same) >= 2);   % find cols of ap with at least 2 such
    if ~isempty(matches)    % at least one col has 2 matches
        ngroups = ngroups+1;   % so add it to the result
        groups{ngroups} = [k k+matches];
    end
end
groups = groups(1:ngroups);   % trim results to the part that was used

Best Answer

Related Solutions

MATLAB: Split the 132×10 cells into 1×10 arrays

MATLAB: Search nx3 array row-wise for 2 equal elements

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