inverse numpy's bincount()

inverse_numpy_bincount.py

import numpy as np
import itertools
from timeit import timeit

arr = np.random.randint(3, size=100, dtype='uint8')

def method_me(arr):
    return np.array(
        tuple(itertools.chain.from_iterable(
            itertools.repeat(index, value)
            for index, value in enumerate(arr)
        )),
        dtype=np.uint8
    )

def method_hayataka(arr):
    return np.repeat(np.arange(arr.size), arr)


def method_eelco(arr):
    p = np.cumsum(arr)
    i = np.zeros(p[-1], np.uint8)
    np.add.at(i, p[:-1], 1)
    return np.cumsum(i)


print('me:', timeit(lambda: method_me(arr), number=2000))
print('hayataka:', timeit(lambda: method_hayataka(arr), number=2000))
print('eelco:', timeit(lambda: method_eelco(arr), number=2000))