group coordinates according to the value of z

Hi. Attached is the file "coordinates.txt".

I would like to group the coordinates of an mx3 array based on the value of z and place each group of values (with equal z) inside different cells.

The image shows what I would like to do.

I am starting like this. How can I modify it?

coordinate = importdata('coordinate.txt');

z_coordinate = coordinate(:,3);

for jj = 1:length(z_coordinate)

    Group{jj} = z_coordinate(jj,:);

end

Answer 1

[Askic V]

I would start like this:

coordinate = importdata('coordinate.txt');
z_coordinate = unique(coordinate(:,3));
N = numel(z_coordinate);
cell_group = cell([],N);
for ii = 1: N
    ind = find(coordinate(:,3) == z_coordinate(ii));
    cell_group{ii} = coordinate(ind,1:2);
end

cell_group{1}

This will produce 1x6 cell array:

cell_group =

  1×6 cell array

    {9×2 double}    {6×2 double}    {13×2 double}    {11×2 double}    {3×2 double}    {11×2 double}

I'm sure there is even more efficient way to do this, but there are real gurus here who can help.

ans =

   205   329
   205   328
   205   327
   205   326
   205   325
   205   324
   205   323
   205   322
   206   330

[Alberto Acri]

I thank you @Askic V! If I wanted to keep within each cell the z coordinates as well?

[Askic V]

in that case, the line

cell_group{ii} = coordinate(ind,1:2);

becomes

cell_group{ii} = coordinate(ind,:);

First element of cell_group is then:

ans =

  205.0000  329.0000    5.9649
  205.0000  328.0000    5.9649
  205.0000  327.0000    5.9649
  205.0000  326.0000    5.9649
  205.0000  325.0000    5.9649
  205.0000  324.0000    5.9649
  205.0000  323.0000    5.9649
  205.0000  322.0000    5.9649
  206.0000  330.0000    5.9649