MATLAB: Splitting a vector at sign change

MATLABvector separation

Hi!

I have a vector with values > 0 and values < 0 such as for example:

K = [1 2 3 4 5 6 7 8 -1 -2 -3 -4 -5 -6 -7 -8 1 2 3 4 5 6 7 8] and so on….

I want to split this vector to n new vectors where the sign changes from + to – and vice versa such that:

N1 = [1 2 3 4 5 6 7 8]

N2 = [-1 -2 -3 -4 -5 -6 -7 -8]

N3 = [1 2 3 4 5 6 7 8]

The K vector does not have a set number of positive or negative values between each sign change.

Any suggestions?

Regards

Best Answer

K = [1 2 3 4 5 6 7 8 -1 -2 -3 -4 -5 -6 -7 -8 1 2 3 4 5 6 7 8] ; 
K = K' ; 
S = sign(K) ;
C = mat2cell(S, diff([0; find(diff(S)); size(S,1)]));
L = cellfun(@numel,C) ;
iwant = mat2cell(K,L) ; 
celldisp(iwant)

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Start with "If an entry in B is greater than or equal to zero": You can either run a loop over all elements of B or use "logical indexing":

% Linear indexing:
for k = 1:numel(B)
   if B(k) >= 0
     ...
   end
end

Or two indices for rows and columns:

for r = 1:size(B, 2)
  for c = 1:size(B, 1)
    if B(r, c) >= 0
       ...
    end
  end
end

Or "logical indexing":

index = (B >= 0);
disp(B(index))

Now try to use this to modify B. Use the mentioned terms to search in the documentation and in the internet.

Best Answer

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