As the data is not given, I have created some random data...check the code:
v = [1 2 3 0 0 0 0 0 2 3 4 0 0 0 0 0 4 5 6 7 0 0 0 0 1 1 1]';
A = rand(27,4) ;
A(:,4) = v ;
w = [false; v~=0 ;false];
starts = find(w(2:end) & ~w(1:end-1)); %Get starts of runs of non-zeros
ends = find(~w(2:end) & w(1:end-1))-1; % Get ends of runs of non-zeros
result = arrayfun(@(s,e) A(s:e,1:3), starts, ends, 'uniformout', false); % extract the respective parts
iwant = cellfun(@mean,result,'uniformout',false)
