Efficiency fix

Hi, another efficiency fix needed. this one runs over 20 second everytime. would be a big help if that nested loop could be shortened somehow.Thanks!

counter3 = 1;
for n = 1: length(mymatrix2(1,:))
  for p = 1:length(mymatrix2(1,:))
    if abs (mymatrix2(1,n) - mymatrix2(1,p)) == 1;
      if mymatrix2(2,n) >= mymatrix2(2,p)    ;
        if ismember ( mymatrix(1,n), replacewith) == false
          replacewith(counter3) = mymatrix2(1, n);
        end
      elseif mymatrix2(2,p) >=mymatrix2(2,n);
        if ismember (mymatrix(1,p), replacewith) == false
          replacewith(counter3) = mymatrix2(1,p);
        end
      end
      counter3 = counter3 +1;
    end
  end
end

[Walter Roberson]

Andy, I had to edit a fair bit to make the code readable. Please be especially careful about trailing blanks on the line: if they fall in just the wrong place then things might look right as you enter the code in, but look bad in the finished message. Best is not to have trailing blanks.

I left in the semi-colon you have at the end of an "if" and an "elseif" line. Those semi-colon are not necessary.

Answer 1

[Jan]

Some simplifications at first:

counter3 = 1;
len = size(mymatrix2, 2);
for n = 1:len
  a = mymatrix(1, n);
  for p = 1:len
    b = mymatrix2(1,p);
    if abs(a - b) == 1
      if mymatrix2(2,n) >= mymatrix2(2,p)
        if ~any(a == replacewith)
          replacewith(counter3) = a;
        end
      elseif mymatrix2(2,p) >= mymatrix2(2,n);
        if ~any(b == replacewith)
          replacewith(counter3) = b;
        end
      end
      counter3 = counter3 + 1;
    end
  end
end

But I'm sure this profits from vectorization. Please post meaningful test data - a RAND is preferred.