How do I add a matrix to another matrix with different sizes?

I got the following problem. if I have the following two matrices:

A=[1  2  1
   3  4  1
   7  8  1]

B=[1  2  0
   2  6  0
   3  4  0
   4  9  0
   5  2  0
   6  1  0
   7  8  0]

I need to add matrix A to matrix B with remaining the rows of matrix B. Only when the first two elements are the same, the row should be replaced. I need a matrix:

C=[1  2  1
   2  6  0
   3  4  1
   4  9  0
   5  2  0
   6  1  0
   7  8  1]

I hope someone could help me with this.

Answer 1

[Andrei Bobrov]

EDIT

[ii,jj] = ismember(B(:,1:2),A(:,1:2),'rows');
C = B;
C(ii,3) = A(jj(ii),3);

[Glenn Roumen]

I editted the question because I need something else.

[Andrei Bobrov]

EDIT

[Glenn Roumen]

Thank you very much!

Answer 2

[Azzi Abdelmalek]

   B(A(:,1),:)=A

[Glenn Roumen]

I editted the question because I need something else.

[Azzi Abdelmalek]

Glenn, if you need something else, you should post another question. Please post your initial question and add a question as a comment

Answer 3

[Pourya Alinezhad]

if you want to add matrix A to first raw's of B you can use the following code:

C=zeros(size(B));
C(1:size(A,1),:)=A;
C(size(A,1)+1:end,:)=B(size(A,1):end,:)

but as i can see in C matrix you mentioned every raw of A is in it's first index value raw.for example if we have [3 1 1] so the raw will appear in third raw and [7 1 1] will appear in seventh raw.for this purpose you can use below code:

 C=B;
  for i=1:size(A,1)
    C(A(i,1),:)=A(i,:);
  end

[Glenn Roumen]

I editted the question because I need something else.

Answer 4

[Pourya Alinezhad]

C=B;
for i=1:length(B)
    for j=1:length(A)
    if A(j,1:2)==B(i,1:2)
    C(i,:)=A(j,:)
    end
    end
end

[Pourya Alinezhad]

and the result is as you want : C =

     1     2     1
     2     6     0
     3     4     1
     4     9     0
     5     2     0
     6     1     0
     7     8     1