how to choose from a list based on sign changes in the list?

user_17251744 0
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I have a list and inside of the list, the values and their signs are changing intermittently. I would like to define a function to extract from the list in every two consecutive sign-changing (Let's say zero-crossing points).

n = 5 #a number which comes from another list and here is written to make this example
List_1 = [-1.,-0.89, -0.77,-0.667, -0.55, -0.44,-0.333, -0.22, -0.111,0.,1,1.333,1.66,2,2.3,2.66,3.3, 3.667, 4,-30,-26.77,-23,-20.33-17.11,-13.8,-10,-7.44,-4.22, -1.,30,37.5,45,52.5,60]

def list_excluder:
   for i in range(n):
      zero_crossings = np.where(np.diff(np.sign(list_1[i])))[0]
      GG = list_1[i][zero_crossings[i-1]:zero_crossings[i]]
      ls.append(GG)

expected result:

ls = [[-1.,-0.89, -0.77,-0.667, -0.55, -0.44,-0.333, -0.22, -0.111,0.,1,1.333,1.66,2,2.3,2.66,3.3, 3.667, 4],[-30,-26.77,-23,-20.33-17.11,-13.8,-10,-7.44,-4.22, -1.,30,37.5,45,52.5,60.]]
numpy python
2 Answers

I think I understand just from looking at your input output sample.

List_1 = [-1.,-0.89, -0.77,-0.667, -0.55, -0.44,-0.333, -0.22, -0.111,0.,1,1.333,1.66,2,2.3,2.66,3.3, 3.667, 4,-30,-26.77,-23,-20.33,-17.11,-13.8,-10,-7.44,-4.22, -1.,30,37.5,45,52.5,60]
a = np.array(List_1)
i = np.flatnonzero((a[:-1] - a[1:]) > 0)
np.split(a, i+1)

Output:

[array([-1.   , -0.89 , -0.77 , -0.667, -0.55 , -0.44 , -0.333, -0.22 ,
        -0.111,  0.   ,  1.   ,  1.333,  1.66 ,  2.   ,  2.3  ,  2.66 ,
         3.3  ,  3.667,  4.   ]),

 array([-30.  , -26.77, -23.  , -20.33, -17.11, -13.8 , -10.  ,  -7.44,
         -4.22,  -1.  ,  30.  ,  37.5 ,  45.  ,  52.5 ,  60.  ])]
user_149232270

I guess, here is your answer based on the explanation which was given by you:

def finding_bends(data, arr):
    zero_crossings = np.where(np.diff(np.sign(arr)))[0]
    zero_crossings = np.array(zero_crossings)
    BENDs = []
    
    for i in range(len(zero_crossings)-1):
#         print(i)
        BENDs.append(data[zero_crossings[i]:zero_crossings[i+1]])
        
    return BENDs
user_138905960
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