Question

We have a matrix:

Index:    1 2 3 4 5 6 

Elements:
          0 2 0 5 9 8 
          1 0 5 0 5 4
          0 1 0 0 6 0 

Is it possible to be sorted by size of different elements per column?
Result should be like this:

  Index:     5 2 6 1 3 4 

  Elements:
             9 2 8 0 0 5 
             5 0 4 1 5 0
             6 1 0 0 0 0 

Thank you in advance.

Answer 1

With “length” and “unique” functions you can retrieve the number of different values of each column (including zero), for example:

for n=1:size(a,2)
  b(n)=length(unique(a(:,n)));
end

If you want to ignore zeros you could use

b(n)=sum(unique(a(:,n)) ~= 0);

Which gives an array with the number of different elements of each column:

b =    1     2     1     1     3     2

Then you can sort this array and use the ordered indexes to sort your matrix:

[~, index]=sort(b, 'descend');
result = a(:, index)