Count consecutive occurences of values varying in length in a numpy array

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If you already have a numpy array, this is probably going to be faster:

>>> condition = np.array([True,True,True,False,False,True,True,False,True])
>>> np.diff(np.where(np.concatenate(([condition[0]],
                                     condition[:-1] != condition[1:],
                                     [True])))[0])[::2]
array([3, 2, 1])

It detects where chunks begin, has some logic for the first and last chunk, and simply computes differences between chunk starts and discards lengths corresponding to False chunks.

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