Need to access only few samples from and an array

Hi I have a matrix and instead of traversing sequentially I need to traverse randomly. So I use another array to random the index of the matrix and use if for traversing. Now From that pseudorandom i do not want one row of the matrix to be processed and I am not getting desired result. Can you help me with it. Below is the code and explanation of the same.

 a=[10 12 16 15; 3 4 8 0; 14 11 4 1; 7 6 15 9;]
b=a';
d=b(:)';
[r,c]=size(a);
seed_key = 123456; %  key
rng(seed_key); % seed the random number generator
idxs1 = randperm(r*c);
cnt_rnj=1;
half=r*c/2;
halfend=half+r;
inx=find(idxs1>half & idxs1<halfend+1);
for i=1:length(d)

   if (i~=idxs1(inx(cnt_rnj)))
       % idd(i)=1; //to check how the loop is processing

    else
        %idd(i)=2; // to check how the loop is processing
        cnt_rnj=cnt_rnj+1
        YN=i
    end
end

Basically if it is a 4x4 matrix I do not wanted index position 9,10,11,12 to be processed. If I had to do it sequentially it is not an issue but as I am traversing the randomly the index position will not be in order in the idxs1 matrix. Here for example matrix inx has the position of [9,10,11,12] of array d as [1,7,9,11]. Using the if (i~=idxs1(inx(cnt_rnj))) it evaluates position 9,11,12 but misses 10th index. Can you please help me to solve this.

Answer 1

[dpb]

"...I do not wanted [sic] index position 9,10,11,12 to be processed."

If you mean original indices then just remove them from the index vector before processing the remainder--

ixExclude=[9:12];                       % the exclusion set
idxs1 = randperm(r*c);
idx=setdiff(idxs1,ixExclude,'stable');  % the permuted set excluding unwanted
for i=1:length(idx)
  ...
  do whatever with those wanted here
  ...

More than likely you can eliminate the for...end loop over the indices and use the selection index vector in Matlab array syntax operations as well.

[Amishi]

Thank you so much:) Did not think this way. Sure I shall check on your suggestion as well