MATLAB: Sequence/pattern problem

Question

Hi, I have a problem.

A=[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ];

From above A, I want B like below :

B=[1 2 3 4 8 9 10 11 15 16 17 18 ];

Now, if my A is like below:

A=[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24];

Then B will be like below:

B=[1 2 3 4 8 9 10 11 15 16 17 18 22 23 24];

Which means. first four elements of A will be in the B; then the next three elements of A will not be in B; then next 4 elements of A will be in B; and so on so forth..

Last few elements of A will be / will not be in the B depend on if they are in the sequence or not.

I tried to explain the case study above. Please let me know if something is not clear.

Thanks in advance.

Answer 1

A=[1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20 21 22 23 24 ];
B1 = chop43(A(1:20))
B1 = 1×12
     1     2     3     4     8     9    10    11    15    16    17    18
B2 = chop43(A)
B2 = 1×15
     1     2     3     4     8     9    10    11    15    16    17    18    22    23    24
function B = chop43(A)
    full_blocks = floor(length(A)/7);
    blocksizes = repmat([4 3], 1, full_blocks);
    leftover = length(A) - full_blocks*7;
    if leftover > 0 & leftover <= 4
        blocksizes(end+1) = leftover;
    elseif leftover >= 5
        blocksizes(end+1:end+2) = [4, leftover-4];
    end
    blocks = mat2cell(A, 1, blocksizes);
    B = [blocks{1:2:end}];
end