Splitting a vector at sign change

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

Answer 1

[KSSV]

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)

[Stephen23]

A simpler and more efficient approach to get the run lengths:

>> L = diff(find([1,diff(sign(K)),1]))
L =
   8   8   8

[Holmbrero]

Thanks for the input!

I have a follow up question.

I want the values from iwant as a txt. or equal with each cell as a column such that:

iwant(1) iwant(2) iwant(3)

1 -1 1

2 -2 2

3 -3 3

4 -4 4

5 -5 5

6 -6 6

7 -7 7

8 -8 8

And so on. Any suggestions?

Regards,

Answer 2

[Holmbrero]

Works great. Thank you very much!

Answer 3

[Kevin Joshi]

K = [1 2 3 ...
    -1 -2 -3 ...
    -1 -2 -3 -4 ...
    1 2 3 4 5 6 7 8];

%%
m = 1;
n = 1;
x = 1;
y = 1;

for i = 1:length(K)
    if K(i)<0
        s.(['n' num2str(m)])(n) = K(i);
        n = n + 1;
        if (i+1) < length(K) && K(i+1) > 0
            x = x + 1;
            y = 1;
        end        
    else
        s.(['p' num2str(x)])(y) = K(i);
        y = y + 1;
        if (i+1) < length(K) && K(i+1) < 0
            m = m + 1;
            n = 1;
        end
    end
end