Grouping of sub arrays

Dear Matlab community,

This is a toy example to explain my question:

x=[1 1 2 3 3 1 0 4 4 4 1 1 1 1 5 5 0 1 3 3 3 3 1 4 4 4 0 0 1 1 5 6];

I have used the following function to define regions of interest:

[Groups, NumberOfGroups] = bwlabel(x >= 3);

>>NumberOfGroups = 6

>> Groups = [0 0 0 1 1 0 0 2 2 2 0 0 0 0 3 3 0 0 4 4 4 4 0 5 5 5 0 0 0 0 6 6]

I got groups as follows: {(1,1), (2,2,2) (3,3) ,...}

Now, if the end of group 1 is only 2 samples or less from the start of group 2, then the new group will start from the start of group 1 to the end of group 2. The suggested solution must look at all consecutive groups to see if, for example, group 3 was two samples of less from group 2, then the new group will start from the beginning of group 1 to the end of group 3.

I have attached an illustarative image. In this image, the bwlabel resulted in 44 groups, while I want only 6 groups (all near by sub-groups must go to one big group).

Best regards,

Answer 1

[Ameer Hamza]

Are you looking for something like this

x=[1 1 2 3 3 1 0 4 4 4 1 1 1 1 5 5 0 1 3 3 3 3 1 4 4 4 0 0 1 1 5 6];

Groups = bwlabel(x >= 3);

cc = bwconncomp(Groups==0);
idx = cellfun(@numel, cc.PixelIdxList)<=2;
idx = cell2mat(cc.PixelIdxList(idx).');
Groups(idx) = nan;
Groups = fillmissing(Groups, 'next')

Result

>> Groups
Groups =
  Columns 1 through 16
     0     0     0     1     1     2     2     2     2     2     0     0     0     0     3     3
  Columns 17 through 32
     4     4     4     4     4     4     5     5     5     5     0     0     0     0     6     6

or perhaps you also want to do this at the end

Groups = bwlabel(Groups>0)

Result

>> Groups
Groups =
  Columns 1 through 16
     0     0     0     1     1     1     1     1     1     1     0     0     0     0     2     2
  Columns 17 through 32
     2     2     2     2     2     2     2     2     2     2     0     0     0     0     3     3

[MahdiH]

Briliant solution Ameer, many thanks!

[Ameer Hamza]

I am glad to be of help!