Help me avoid this error: Empty matrix: 0-by-1

I have a program like this:

clc

a=[0 0; 150 0.5; 300 0.35; 450 0.253; 600 0.22; 750 0.276; 900 0.183; 1050 0.228; 1200 0.17; 1350 0.207; 1500 0.2; 1650 0.19; 1800 0.187; 1950 0.21; 2100 0.176; 2250 0.197; 2400 0.17]

b=[900 900 750 2100 750 150 150 150 300]'

    for i=1:5

        c=find(a(:,1)==b(i));
        f=a(c,:);
        d(i)=prod(f);

    end
e=sum(d)

My main program for many vectors b with components of a. I want to find e, but few result of c are Empty matrix: 0-by-1

Help me. Thanks.

[Pham]

Thank you for helping me. But I do not understand why in my main program, with 3 value "150 150 150" in vector b, then the vector c is "0.5 Empty matrix: 0-by-7 Empty matrix: 0-by-8", without "0.5 0.5 0.5" ??

Answer 1

[Iain]

Change : d(i) = prod(f); to

 if isempty(f)
  d(i) = NaN;
 else
  d(i) = prod(f);
 end

and e = sum(d) to:

 e = nansum(d);

If NaN isn't convenient, change it for something that is.

Answer 2

[Jan]

d = nan(1, 5);
for i=1:5
  c = (a(:, 1) == b(i));
  if any(c)
    d(i) = prod(a(c, :));
  end
end

[Bachtiar Muhammad Lubis]

Thank you @Jan, you have helped me