problem to write a condition for 'if'

I want to save A_new according to this condition:

If A_new decreases the length of B, I want to save it.

I wrote a code like this but I have a problem to write a condition

A = {[1,2,3,4], [1,2,3,6], [1,2,3,8], [1,2,6,7,8], [1,6,8], [2,3,4,7], [3,4,6], [3,4,6,7], [3,4,6,7,8], [3,6,8], [6,7,8], [1,5]};
B =[1 2; 1 4; 1 8; 1 5; 1 6; 2 7; 2 3; 3 6; 3 8; 3 4; 4 7; 4 6; 7 6; 7 8; 6 8];
B_bk = B;
A_new = cell([],1);
length_B = cell([],1);

%% sort A
[~,I] = sort(cellfun(@length,A));
A = A(I);
C = [];

if isempty(B)==0
    
    for i=1:length(A)
        temp = [A{i} A{i}(1)];
        C = [C;[temp(1:end-1)' temp(2:end)']];
        
        [~,X] = setdiff(sort(B_bk,2),sort(C,2),'rows','stable');
        B = B_bk(X,:);
        length_B{i} = length(B);
        
        %% problem to write condition
        if length_B{i}- length_B{i-1}>0 %%???
            A_new{i} = A{i};
        end
        
    end
    
end

result should be

A_new = {[1,5],[1,6,8],[3,4,6],[3,6,8],[6,7,8],[1,2,3,4],[2,3,4,7]};

I think it would be better way to write this code.

Answer 1

[Birdman]

Try the following code:

A = {[1,2,3,4], [1,2,3,6], [1,2,3,8], [1,2,6,7,8], [1,6,8], [2,3,4,7], [3,4,6], [3,4,6,7], [3,4,6,7,8], [3,6,8], [6,7,8], [1,5]};
B =[1 2; 1 4; 1 8; 1 5; 1 6; 2 7; 2 3; 3 6; 3 8; 3 4; 4 7; 4 6; 7 6; 7 8; 6 8];
B_bk = B;
A_new = cell([],1);
length_B = cell([],1);
%% sort A
[~,I] = sort(cellfun(@length,A));
A = A(I);
C = [];
    for i=1:length(A)
        temp = [A{i} A{i}(1)];
        C = [C;[temp(1:end-1)' temp(2:end)']];
        
        [~,X] = setdiff(sort(B_bk,2),sort(C,2),'rows','stable');
        B = B_bk(X,:);
        length_B{i} = length(B);
        if i==1
            A_new{i} = A{i};
        end
        %% problem to write condition
        if i>1
            if length_B{i-1}- length_B{i}>0 %%???
                A_new{i} = A{i};
            end
        end
    end 
A_new=A_new(~cellfun(@isempty,A_new))