Extract vector parts around index under boolean conditions

Hello everybody,

I am trying to extract parts of a signal that meet a certain condition (boolean true) and save them into individual vectors.

Lets say i have a testvector:

testvector = [0 0 1 0 0 0 1 1 1 1 1 1 1 1 0 0 0 1 0 0 1];

Iterating through the signal, if the index is true, I want to check if:

• i-3 positions are 0 (condition1)
• i+5 positions are 1 (condition2)

If both conditions are true, I would like to extract this part of the signal, like mentioned earlier.

Concerning my testvector, due to my conditions there is supposed to be exactly one part to be extracted:

testvector(4:12)

Until now, I've tried the following without success:

values=[];
for i=4:numel(testvector)
    if testvector(i)==1
        buff1 = i-3;
        buff2 = i+5;
        for k=buff1:1:(i-1)
            values = [values, testvector(k)];
            if any(values)
                values(end) = [];
                break
             elseif length(values)>3
                 break
            end
        end
        
        for k=i:1:buff2
            values = [values, testvektor(k)];
            if any(values)
                break
            elseif buff2 > numel(testvektor)
                break
            elseif (length(values)>10)
                continue
            end
        end
        
        new = [new, testvektor(i)]
    end
end

So far, I have no idea how to automatically construct a new vector each time the conditions are met and a part of the signal is extracted.

Thank you in advance, every help is highly appreciated!

Answer 1

[Guillaume]

One way:

testvector = repmat([0 0 1 0 0 0 1 1 1 1 1 1 1 1 0 0 0 1 0 0 1], 1, 3);  %replicate your demo vector so that there is more than one segment to extract

before = movsum(testvector(1:end-5), [3 0], 'Endpoints', 'discard');  %sum of 3 elements before + current element. Will be 1 if a 1 is preceded by three 0s
after = movsum(testvector(4:end), [0 5], 'Endpoints', 'discard');     %sum of 5 elements after  + current element. Will be 6 if a 1 is followed by five 1s
indices = find(before == 1 & after == 6 & testvector(4:end-5) == 1);  %construct a row vector of indices where the condition is true
segments = testvector(indices + (0:9)')   %extract all segments as column vectors

[moar0504]

Sir, you are a genius!

Thank you very much for providing a quite simple as also logical solution!

[Guillaume]

On thing that puzzles me about your requirements is that the segments to be extracted are always going to be [0 0 0 1 1 1 1 1 1], so why bother with the extraction? In any case, my answer gives you the starting locations of the segments (in indices) which is probably more useful.