Thread Subject:

Finding the longest length of zero's...

Hello,

I have a huge single column set of data, and within this are intervals of zero's, with each interval a different length.

I used find(A==0) , and it returns a vector of the locations of all zero's. I am ultimately interested in finding the starting and stopping indices of the longest sized interval of zero's.

Can anyone provide tips on how to approach this?

Thank you!

Do you have the Image Processing Toolbox? Is so, it's trivial. Just
call bwlabel and regionprops then pull out the biggest object. It
doesn't matter that it's a 1D "image" instead of a 2D image.

ImageAnalyst <imageanalyst@mailinator.com> wrote in message <2b1bac7a-a751-4341-b025-2e251f6bbdb7@z25g2000vbk.googlegroups.com>...
> Do you have the Image Processing Toolbox? Is so, it's trivial. Just
> call bwlabel and regionprops then pull out the biggest object. It
> doesn't matter that it's a 1D "image" instead of a 2D image.

If not, you can use your logical result this way:

B = A==0;
st = findstr(B.',[0 1])+1; % If A is a column vector. The starting points
ed = findstr(B.',[1 0]); % The ending points.
% Now, assuming you take care of any boundary problems (I leave to you)....
[idx,idx] = max(ed-st);
idx = st(idx)

"D " <dale.kim@gatech.edu> wrote in message <hvbjmg$303$1@fred.mathworks.com>...
> Hello,
>
> I have a huge single column set of data, and within this are intervals of zero's, with each interval a different length.
>
> I used find(A==0) , and it returns a vector of the locations of all zero's. I am ultimately interested in finding the starting and stopping indices of the longest sized interval of zero's.
>
> Can anyone provide tips on how to approach this?
>
> Thank you!
- - - - - - - - -
  You can also do it this way. Let d be the column vector of data.

 t = diff([false;d==0;false]);
 p = find(t==1);
 q = find(t==-1);
 [maxlen,ix] = max(q-p);
 first = p(ix);
 last = q(ix)-1;

maxlen is the length of the longest consecutive series of zeros, first is the index of its beginning, and last is the index of its end.

Roger Stafford

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <hvbpaf$hlf$1@fred.mathworks.com>...
> "D " <dale.kim@gatech.edu> wrote in message <hvbjmg$303$1@fred.mathworks.com>...
> > Hello,
> >
> > I have a huge single column set of data, and within this are intervals of zero's, with each interval a different length.
> >
> > I used find(A==0) , and it returns a vector of the locations of all zero's. I am ultimately interested in finding the starting and stopping indices of the longest sized interval of zero's.
> >
> > Can anyone provide tips on how to approach this?
> >
> > Thank you!
> - - - - - - - - -
> You can also do it this way. Let d be the column vector of data.
>
> t = diff([false;d==0;false]);
> p = find(t==1);
> q = find(t==-1);
> [maxlen,ix] = max(q-p);
> first = p(ix);
> last = q(ix)-1;
>
> maxlen is the length of the longest consecutive series of zeros, first is the index of its beginning, and last is the index of its end.
>
> Roger Stafford



Thank you all!