Count number of consecutive 1's within a block

If x= 0 0 0 0 1 1 1 1 0 1 1 1 0 1 1 0 1 0 then the intended output would be y=4 3 2 1. It would also be useful if I had someway of knowing when each group started, as in 4 having begun at the 5th point and 3 at the 10th etc.

Many thanks in advance!

Answer 1

[Roger Stafford]

Let x be the given row vector.

   f = find(diff([0,x,0]==1));
   p = f(1:2:end-1);  % Start indices
   y = f(2:2:end)-p;  % Consecutive ones’ counts

[DoyleDk]

Perfect, just saved me a lot of headaches, thank you kindly

[Maciej Maj]

what does the f vector contain? (p and y I understand)

[Bruno Luong]

The array f contains the indexes in x where the transitions 0->1 or 1->0 occur.

f alternates p (0->1) and y+p (1->0).

[Maciej Maj]

@Bruno Luong thank you!

I am having problems with how to convert the Accepted answer code so that the p and y vectors now start checking for 0 instead of 1.

In other words how do i change the code so:

• p returns the indices of 1->0 transition
• y returns the lengths of the consecutive sequences with their elements equal to 0.

I'll be grateful!

[Bruno Luong]

For detection of sequence of 0s

    f = find(diff([1,x,1]==0));
    p = f(1:2:end-1);  % Start indices
    y = f(2:2:end)-p;  % Consecutive zeros’ counts

[Tomos Winstanley]

How would this code be adjusted to include a gap of zero for 11 in the code so that the output vector is the same length?

[Image Analyst]

What does that mean? I have no idea what "include a gap of zero for 11 in the code" means. Please explain. What is a gap of zero? A zero width gap? What is that? What's eleven?

Answer 2

[Image Analyst]

Use regionprops():

x= [0 0 0 0 1 1 1 1 0 1 1 1 0 1 1 0 1 0]
% Label each separate region.
[labeledX, numRegions] = bwlabel(x)
% Get lengths of each region
props = regionprops(labeledX, 'Area', 'PixelList');
regionLengths = [props.Area]
for k = 1 : numRegions
  fprintf('Region #%d is %d elements long and starts at element #%d\n',...
    k, regionLengths(k), props(k).PixelList(1));
end

You'll see in the command window:

regionLengths =
     4     3     2     1
Region #1 is 4 elements long and starts at element #5
Region #2 is 3 elements long and starts at element #10
Region #3 is 2 elements long and starts at element #14
Region #4 is 1 elements long and starts at element #17

[DoyleDk]

This looks close to what I want, unfortunately I'm working with the base program without any add-ons. Thank you though!