Retrieving array elements with an array of frequencies in NumPy

Question

I have an array of numbers, a. I have a second array, b, specifying how many times I want to retrieve the corresponding element in a. How

Answer 1

A really inefficient way to do that is this one :

import numpy as np

a = np.arange(5)
b = np.array([1,0,3,2,0])

res = []
i = 0
for val in b:
    for aa in range(val):
        res.append(a[i])
    i += 1
print res