MATLAB: How to search for a previous element that is equal in prior loop iteration

Question

I have a Matrix called A as below

[1  1  3;
1  2  2;
1  3  3;
2  1  1;
2  2  3;
2  3  2;
2  4  4]

I want to produce a column vector that counts the number of times a value occurs in the 2nd column, I have tried the following function :

function count_stars(A)
total = 0;
for i = 1:size(A,1)
    total = total + (A(i,2)==A(:,2));
   end
total

This counts the number of matching values in the entire column e.g.

       2
       2
       2
       2
       2
       2
       1

What I am wanting is to match to values between 1:i only rather than the entire column so that the output looks like this

1
1
1
2
2
2
1

Any insights you are able to share are greatly appreciated!

Answer 1

hello tim try this code

a=[1  1  3;
1  2  2;
1  3  3;
2  1  1;
2  2  3;
2  3  2;
2  4  4];
for i=1:size(a,1)
    [r,c]=find(a(1:i,2)==a(i,2));
    b(i,1)=length(r);
end
b