Replacing small sections of a logical vector

I'm working with EMG data to determine when muscles activate in a group of disabled people.

After data processing I end up with a logical vector, of 1s where the muscle in 'on', and 0s where the muscle is 'off', for example:

    EMG = 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Periods of three 1s or less in a row are likely to be artefact, and I need to replace them with 0s. E.g. to make the above into:

EMG = 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Any help is greatly appreciated!

Answer 1

[Image Analyst]

It's a one-liner if you have the Image Processing Toolbox since there is a function made specially to do that operation:

EMG = bwareaopen(EMG, 4);  % Keep runs of 1's that are 4 or longer.

Answer 2

[Alexandra Harkai]

There are a few different ways to do it.

This method may be frowned upon, but it nonetheless produces the required output:

n = 3; % max length of artefact periods
s = char(EMG+65); % converting 0-1 data to A-B string
for j=1:n
  % get rid of periods of length j
  s = strrep(s, ['A', repmat('B',1,n), 'A'], [repmat('A',1,n+2)]);
end
res = double(s)-65; % converting back to logical values

Answer 3

[Andrei Bobrov]

v = bwlabel(EMG);
EMG(ismember(v,find(accumarray(v(:)+1,1)<=3)-1)) = 0;

Answer 4

[Jan]

With http://www.mathworks.com/matlabcentral/fileexchange/41813-runlength :

[B, N]    = RunLength(EMG);
B(N <= 3) = 0;
EMG2      = RunLength(B, N);