Finding a break in continuous indices in a numpy array-CodePudding

I have a conditional statement for an array A(assume it is A>10) and I get this boolean result.

array([False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True, False, False, False, False,
       False, False, False, False, False, False,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False])

Now I am finding the indices where the values are True. So I get this array.

array([20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
       37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 60, 61, 62, 63,
       64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80,
       81, 82, 83, 84, 85, 86, 87, 88, 89, 90])

What I need to do is to find the start index and end index of continuous indices. For example in the above array, the start index of the first continuous indices is 20 and the end index is 49. Similarly, the start index of the second set of continuous indices are 60 and the end index is 90.

So to summarize, my output should be :

start_indices = array([20,60])

end_indices = array([49,90])

How to do this?

CodePudding user response：

import numpy as np

changes = np.where(np.diff(A))[0] # Gets the actual array out of a tuple
start = changes[::2]   1
end = changes[1::2]

CodePudding user response：

Here is a solution using groupby and accumulate from itertools:

from itertools import groupby, accumulate
indices = list(accumulate(len(list(g)) for i,g in groupby(a)))
starts = indices[:len(indices)//2*2:2]
stops = [i-1 for i in indices[1::2]]

NB. it works with any iterable, not only numpy arrays.

output:

>>> starts
[20, 60]
>>> stops
[49, 90]