How to implement approx_percentile UDAF

[superrookiem]

SQL Like:
select approx_percentile(c1, 0.1) from testtable;

Python Like:
import numpy as np

a = np.array([1,2,3,4,5,6,7,8,9,10])

print(np.median(a))
print(np.percentile(a,10))
print(np.percentile(a,20))
print(np.percentile(a,30))
print(np.percentile(a,40))
print(np.percentile(a,50))
print(np.percentile(a,60))
print(np.percentile(a,70))
print(np.percentile(a,80))
print(np.percentile(a,90))

Thanks!