What code would I use to find the first 0 then count from there?

I have a set of data which contains a block of zeros which I have wrote this code to count the zeros for:

for i=7:length(mydata)
    no_of_zeros = size(mydata{i,1},1) - nnz(mydata{i,1}(:,5)); %number of zeros
    no_of_frames = (no_of_zeros/4) % number of frames 
    time = ((no_of_frames/fps)/2) % time up
    jumph(i,1)=((a*(time*time))/2) % jump height
end

However, some of the data has 2 blocks of zeros as they stepped off the force plate early so matlab includes these 0's in its calculation. So I need matlab to find the first zero in the column then count from there until the zeros stop and change to numbers and use that amount of zeros in the calculations.

How would I do this?

Answer 1

[Image Analyst]

Do you have the Image Processing Toolbox? You can find all the zeros stretches like this:

labeledSignal = bwlabel(mydata == 0);
% Measure lengths of all zero stretches.
measurements = regionprops(labeledSignal, 'Area', 'PixelIdxList');
% Extract from structure into a simple array of lengths.
lengthsOfAllZeroSegments = [measurements.Area];
% See where each segment of zeros starts and stops.
for k = 1 : length(lengthsOfAllZeroSegments )
  startingElement(k) = measurements(k).PixelIdxList(1);
  endingElement(k) = measurements(k).PixelIdxList(end);
end

If you want, you can throw out small stretches before measuring their lengths by using bwareaopen().

Answer 2

[Walter Roberson]

Lvec = logical(mydata{i,1}(:,5));
z_nz_pos = strfind(Lvec, [1 0]);
nz_z_pos = strfind(Lvec, [0 1]);
no_of_zeros = nz_z_pos(1) - z_nz_pos(1);

Caution: this code will need to be adjusted if there is the possibility that the data starts with zeros, or ends with zeros that need to be considered (e.g., landed off of the plate), or is all zero or is all non-zero. The modification for starting or ending with 0 or all 0 is fairly easy, but what should be done for the no-zero case?