Vectorised non zero groups in numpy array

Question

Say you have 1d numpy array:

[0,0,0,0,0,1,2,3,0,0,0,0,4,5,0,0,0]

How would you create the following groups without using for loop?

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

Paul Panzer · Accepted Answer · 2019-04-04 15:26:32Z

2

Here's one way using np.split:

a
# array([0, 0, 0, 0, 0, 1, 2, 3, 0, 0, 0, 0, 4, 5, 0, 0, 0])
### find nonzeros
z = a!=0
### find switching points
z[1:] ^= z[:-1]
### split at switching points and discard zeros
np.split(a, *np.where(z))[1::2]
# [array([1, 2, 3]), array([4, 5])]

answered Apr 4, 2019 at 15:26

Paul Panzer

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Harry Over a year ago

Is there a way to get the indexes?

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