Python code for counting number of zero crossings in an array

Question

I am looking to count the number of times the values in an array change in polarity (EDIT: Number of times the values in an array cross zero).

Suppose I have an array:<

Answer 1

You can achieve it using list comprehension:

myList = [80.6, 120.8, -115.6, -76.1, 131.3, 105.1, 138.4, -81.3, -95.3,  89.2, -154.1, 121.4, -85.1, 96.8, 68.2]
len([x for i, x in enumerate(myList) if i > 0 and ((myList[i-1] > 0 and myList[i] < 0) or (myList[i-1] < 0 and myList[i] > 0))])