Custom Dendrogram Ordering Implementation

Hi,I'm trying to implement a custom ordering of a dendrogram (obtained using the linkage function) based on the rule that the "highest" branch has to be always on the right side. As an example:

%generate a tree using linkage
rng('default'); %for reproducibility
X = rand(10,2);
D = pdist(X);
tree = linkage(D,'average');

%my desired order
myOrd = [1,4,5,8,9,2,10,3,6,7];

%plot
figure();
subplot(2,1,1);
    dendrogram(tree);
    title('Default leaf order');
subplot(2,1,2);
    dendrogram(tree,'Reorder',myOrd);
    title('Desired leaf order');

Do you have any idea for a more efficient implementation?

Thank you

Answer 1

[Massimo Zanetti]

Apparently, none of the available functionalities of optimalleaforder does the work. So here it is a function that runs through the rows of the tree matrix generated by linkage and produces your output.

function c = binOrd(tree)

      p = size(tree,1);
      c = zeros(1,p+1);
      k = 0;

      recBin(p);

      function recBin(r)
          x = tree(r,1:2)-p-1;
          if x(1)<=0
              c(k+1) = tree(r,1);
              k = k+1;
          else
              recBin(x(1));
          end
          if x(2)<=0
              c(k+1) = tree(r,2);
              k = k+1;
          else
              recBin(x(2));
          end
      end

end

To get your desired rightmost binary ordering, run dendogram with 'Reorder' set as the output of the binOrd function:

tree = linkage(D,'average');
myBinOrder = binOrd(tree);
dendrogram(tree,'Reorder',myBinOrder);

[Daniele]

Thank you, that is exactly what I need and it is super-fast. Recursive functions are really powerfull.