find consecutive nonzero values

Question

I am trying to write a simple MATLAB program that will find the first chain (more than 70) of consecutive nonzero values and return the starting value of that consecutive chain.

I am working with movement data from a joystick and there are a few thousand rows of data with a mix of zeros and nonzero values before the actual trial begins (coming from subjects slightly moving the joystick before the trial actually started).

I need to get rid of these rows before I can start analyzing the movement from the trials.

I am sure this is a relatively simple thing to do so I was hoping someone could offer insight. Thank you in advance

EDIT: Here's what I tried:

s = zeros(size(x1)); 

for i=2:length(x1) 
    if(x1(i-1) ~= 0) 
        s(i) = 1 + s(i-1); 
    end 
end 

display(S); 

for a vector x1 which has a max chain of 72 but I dont know how to find the max chain and return its first value, so I know where to trim. I also really don't think this is the best strategy, since the max chain in my data will be tens of thousands of values.

Answer 1

You don't need to use an auxiliary vector to keep track of the index:

for i = 1:length(x)
    if x(i) ~= 0
            count = count + 1;
    elseif count >= 70
            lastIndex = i;
            break;
    else
            count = 0;
    end

    if count == 70
           index = i - 69;
    end
end

To remove all of the elements in the chain from x, you can simply do:

x = x([lastIndex + 1:end]);

EDIT (based off comment):
The reason that the way you did it didn't work was because you didn't reset the counter when you ran into a 0, that's what the:

else
   count = 0;

is for; it resets the process, if you will. For some more clarity, in your original code, this would be reflected by:

  if x1(i-1) ~= 0 
        s(i) = 1 + s(i-1); 
  else
        s(i) = 0;
  end