How can I discretize data by their sign?

I would like to discretize data by their sign and return the index of 'alternating sign'.

For example if I have a vector:

A = [-2,-1,5,-10,7,3,-9,-12,11];

Their signs are like:

s = sign(A)
[-1,-1,1,-1,1,1,-1,-1,1]

I would like to return:

[1,1,2,3,4,4,5,5,6]

Answer 1

[Stephen23]

A = [-2,-1,5,-10,7,3,-9,-12,11];
B = sign(A);
C = cumsum(logical([1,diff(B)]))

C = 1×9

1 1 2 3 4 4 5 5 6

Answer 2

[Chunru]

A = [-2,-1,5,-10,7,3,-9,-12,11];
s = sign(A)

s = 1×9

-1 -1 1 -1 1 1 -1 -1 1

s1 = [1 diff(s)~=0]

s1 = 1×9

1 0 1 1 1 0 1 0 1

y = cumsum(s1)

y = 1×9

1 1 2 3 4 4 5 5 6

% [1,1,2,3,4,4,5,5,6]

[Manling Yang]

Thanks! This is really subtle!