MATLAB: Copy certain number from one matrix to another

arrayMATLABmatrix

I have a matrix that i import from xlxs file using the code
function[output] = second()
    [raw] = xlsread('errors168h.xlsx');
    disp(raw)
    A = raw(:,1);
    B = raw(:,2);
    output=[A,B];
   end
and the matrix i got is
A  B
1  1
2  1
3  1
4  2
5  2
6  2
7  1
8  1
9  2
10  2
11  2
How can i copy matrix from second column but only certain number? the other number will be random either 1 or 2. Example
A  B      |     | A  B
1  1  1   |     | 1  1  1
2  1  1   |     | 2  1  1
3  1  1   |     | 3  1  1
4  2  2   |     | 4  2  2
5  2  1   |  OR | 5  2  2
6  2  1   |     | 6  2  1 
7  1  1   |     | 7  1  1
8  1  1   |     | 8  1  1
9  2  2   |     | 9  2  2
10 2  2   |     |10  2  1
11 2  1   |     |11  2  1
If the third row of 2 become 1, the rest of the column will become 1. process repeat until it reach another set of 2. Whenever it read number 1 on column B, it will stop processing and when it will start changing number again when it read 2 on column B. In short, it do like this
 A  B      A  B   C
------    -----------  
 1  1      1  1   1       %copy normally to C
 2  1      2  1   1
 3  1      3  1   1
 4  2      4  2   2       %read 2 at B. random 1 or 2. get 2
 5  2      5  2   1       %read 2 at B. random 1 or 2. get 1
 6  2      6  2   1       %read 2 at B. Follow previous value and set 1


 7  1      7  1   1       %read 1. copy normally value to C
 8  1      8  1   1
 9  2      9  2   1       %read 2 at B. random 1 or 2. get 1 (start process like previous)
10  2     10  2   1       %read 2 at B. Follow previous value and set 1
11  2     11  2   1       %read 2 at B. Follow previous value and set 1

Best Answer

This does the job perfectly, without any explicit loop:
A = [1:12;1,1,1,2,2,2,1,1,2,2,2,1]'
idx = A(:,2)==2 & [true;diff(A(:,2))==1];
idy = ~idx(1)+cumsum(idx);
tmp = accumarray(idy,A(:,2),[],@(n){n});
fun = @(v)[sort(randi(1:2,nnz(v==2),1),'descend');v(v==1)];
out = [A,cell2mat(cellfun(fun,tmp,'UniformOutput',false))]
And tested a few times:
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     2
   5     2     2
   6     2     2
   7     1     1
   8     1     1
   9     2     2
  10     2     2
  11     2     1
  12     1     1
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     2
   5     2     2
   6     2     1
   7     1     1
   8     1     1
   9     2     2
  10     2     1
  11     2     1
  12     1     1
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     1
   5     2     1
   6     2     1
   7     1     1
   8     1     1
   9     2     2
  10     2     1
  11     2     1
  12     1     1
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     2
   5     2     1
   6     2     1
   7     1     1
   8     1     1
   9     2     2
  10     2     1
  11     2     1
  12     1     1
...etc
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