Find sequences where all elements have same sign and then change sign-CodePudding

I have a series of lists with 7 elements (but could be any number). I am trying to find the lists that have all positive elements, all negative elements, and those that change sign at ANY point,

for example [3, 6, 7, -2, -5, -1, -1] or [3, 1, -1, -2, -1, -5, -1].

Note that, though I used integers in my example, the lists are actually made of floats.

I can easily find all lists that are always positive or negative, but how do I find those that change sign (it could go from positive to negative as in example or from negative to positive).

CodePudding user response：

Use the for loop to iterate from 0th element to penultimate element and compare the signs or check if the product of 2 consecutive numbers is less than 0.

If yes, then append the elements in the list.

CodePudding user response：

Assume the Series is

0     [3, 6, 7, -2, -5, -1, -1]
1    [3, 1, -1, -2, -1, -5, -1]
dtype: object

You can try get the sign of each element of list in Series and sum them.

If the result is 7, it means all positive,
If the result is -7, it means all negative
Otherwise, it may change the sign. (considering zero)

m = s.apply(lambda lst: sum(map(np.sign, lst)))

print(m)

0   -1
1   -3
dtype: int64

To consider zero in list, you can join the sign list and check if there is 1,-1 or -1,1

n = s.apply(lambda lst: ','.join(map(str, map(np.sign, lst))))
n = n.str.contains('1,-1|-1,1')

print(n)

0    True
1    True
dtype: bool

If you are not restrict with the 0 place, you can just check if there is 1 and -1 in the sign list

n = s.apply(lambda lst: {1, -1}.issubset(set(map(np.sign, lst))))