Grouping continuous nonzero in a row vector

Dear All,

Is there any MATLAB function to ease grouping continuous nonzero elements of a row vector? I will explain further in the example below:

If I have such a simple row vector: A = [0,0,0,0,3,2,5,2,4,1,5,0,1,2,5,0,0,0,0,0,0,0,0,0,1,1,2,6,3,1]

Then I need to work on each continuous nonzero groups separately, i.e. I need to obtain matrices below to further analyze each group:

A1 = [3,2,5,2,4,1,5] ; A2 = [1,2,5] ; A3 = [3,2,5,2,4,1,5];

Thanks!

Answer 1

[Cedric]

Here is one solution..

 wrap       = [0, A, 0] ;
 temp       = diff( wrap ~= 0 ) ;
 blockStart = find( temp == 1 ) + 1 ;
 blockEnd   = find( temp == -1 ) ;
 blocks     = arrayfun( @(bId) wrap(blockStart(bId):blockEnd(bId)), ...
                        1:numel(blockStart), 'UniformOutput', false ) ;

With that, you get

 >> blocks{1}
 ans =
     3     2     5     2     4     1     5

 >> blocks{2}
 ans =
     1     2     5

 >> blocks{3}
 ans =
     1     1     2     6     3     1

Another solution would be to compute the start and size of clusters of 0's, eliminate the latter from A, and MAT2CELL what remains using proper boundaries based on the aforementioned start and size information.

[Mona Mahboob Kanafi]

Thank you very much man!

[Cedric]

You're welcome.

Answer 2

[Andrei Bobrov]

A = [0,0,0,0,3,2,5,2,4,1,5,0,1,2,5,0,0,0,0,0,0,0,0,0,1,1,2,6,3,1];
ii = zeros(size(A));
jj = A > 0;
ii(strfind([0,jj(:)'],[0 1])) = 1;
idx = cumsum(ii).*jj;

out = accumarray( idx(jj)',A(jj)',[],@(x){x'});

[Mona Mahboob Kanafi]

Hi Andrei, Thanks for your answer. Nice idea, only for the use of accumarray it gives an error

[Andrei Bobrov]

Hi Mona! I corrected.

[Mona Mahboob Kanafi]

Thankss a lot, quite clever!

Answer 3

[Akhlaqur Rahman]

 y = [1 2 1 3 1 4 0 0 0 0 4 5 2 3 0 0 5 4 2 3 0 0 0 4 5 3];
y = padarray(y,[0,3]);
y1 = uint8(y>0);
k = 1;
j = 1;
for i = 1+1:length(y)-1
    if y1(i)>0 && y(i-1)==0
        x1(j) = i;
        j = j+1;
    elseif y1(i)==0 &&y1(i-1)>0
        x2(k) = i;
        k = k+1 ;
    end
end
for i = 1:length(x1)-1
    z{i}=y(x1(i):x2(i)-1);
    cell2mat(z(i))
end

Answer 4

[Emma DeWitt Cotter]

This can also be achieved using the bwconncomp function if you have the Image Processing toolbox. The PixelIdxList field will be a cell containing the list of indices associated with each group of nonzero elements.