How to change an if-condition in a loop by logical indexing to make my code faster?

Hi,

I have got a serious performance problem with the Matlab-code below. It works but the "for"-loop - especially the "if"-condition - is really slow.

How can I rewrite the "if"-condition to make my code faster? Maybe the key is to form a logical index?

Thanks a lot!

My code: - "A.", "B.": structural arrays containing matrices - "C.": structural array containing vectors

for k=1:numel(fields_A) 
      A = A.(fields_A{k}); 
      B = B.(fields_A{k}); 
      C = C.(fields_A{k}); 
      for i = 1:size(A,1) 
                  for j = 1:size(A,1) 
                  if (A(i,:) == B(j,:) & C(i,1) ~= 1), C(j,1)=1;   
                  end 
                  end   
      end 
      A(find(C(:,1)==1),:)=[]; 
      A.(fields_A{k})= A; 
  end

Answer 1

[Daniel Shub]

It is likely that

A(i,:) == B(j,:)

is not doing what you think it is, especially in the context of an if statement. You may want

isequal(A(i,:), B(j, :));

or

all(A(i,:) == B(j,:))

or maybe

any(A(i,:) == B(j,:))

Also, there is no reason to evaluate

C(i,1) ~= 1

inside the j loop. Depending on your data, this could save a significant portion of time or very little. You probably also want to use

&&

instead of

&

since the former shot circuits when possible saving a comparison.

Answer 2

[Andrei Bobrov]

[EDIT]

try

fn = fieldnames(A);
for jj = 1:numel(fn)
  n = fn{jj};
  [a b] = ismember(A.(n),B.(n),'rows');
  C.(n)(b(b ~= 0),1) = 1;
  A.(n) = A.(n)(C.(n)(:,1)~=1,:);
end