Removing consecutive zeros of a certain length

Hi everyone,

I have data consisting of two columns: time and counts. The counts data consists of multiple numbers with some consecutive zeros. How can Matlab find and count the duration of these consecutive zeros and then delete the rows of them if the duration is above a certain value?

Answer 1

[KSSV]

 x = [0 0 0 2 2 0 0 0 3 3 3 3 3 0 0 0 0 ]' ;
transitions = diff([0 ;x == 0; 0]); %find where the array goes from non-zero to zero and vice versa
runstarts = find(transitions == 1);
runends = find(transitions == -1); %one past the end
runlengths = runends - runstarts;
% keep only those runs of length 4 or more:
runstarts(runlengths > 3) = [];
runends(runlengths > 3) = [];
%expand each run into a list indices:
indices = arrayfun(@(s, e) s:e-1, runstarts, runends, 'UniformOutput', false);
indices = [indices{:}];  %concatenate the list of indices into one vector
% Remove those zeros which are consecuitve 3 in number
x(indices) = [] ;

Code taken from here: https://in.mathworks.com/matlabcentral/answers/293926-how-do-i-find-4-or-more-consecutive-zeros-and-replace-these-zero-s

[Debbie Oomen]

Yes I have seen this, however this only involves variable x. Whereas I have variables: time and counts. I can delete the consecutive zeros in my counts row but I also need the time to be adjusted

[KSSV]

Yes....the same can be applied to two columns also...... indices gives you row indices...you remove those rows from your matrix...what else?

[Debbie Oomen]

When I try this:

Data(indices) = [];

it gives me the two columns beneath each other instead of placing them next to each other with the correct rows removed

[Stephen23]

You need to use the indices as row subscripts:

Data(indices,:) = [];

[Debbie Oomen]

Thank you! This works perfectly

Answer 2

[Jan]

What is the "duration"? The number of consecutive elements or does the "time" in the first column matter?

If elements are meant: With https://www.mathworks.com/matlabcentral/fileexchange/41813-runlength:

[B, N] = RunLength(Data(:, 2));
match  = (B ~= 0 | N < 3);
index  = RunLength(match, N);
Data2  = Data(index, :);

This removes all rows, if the number of consecutive zeros in the 2nd column is greater equal 3.

If you do not have a C-compiler installed, use RunLength_M() instead or RunLength() from the same submission. It does exactly the same as the faster C-Mex, but as slower Matlab code.