Numpy gcd function

Question

Does numpy have a gcd function somewhere in its structure of modules?

I\'m aware of fractions.gcd but thought a numpy

Answer 1

In case the desired result is not an element-wise gcd but rather the gcd of all numbers in the array, you may use the code below.

import numpy as np
from math import gcd as mathgcd

def numpy_set_gcd(a):
    a = np.unique(a)
    if not a.dtype == np.int or a[0] <= 0:
        raise ValueError("Argument must be an array of positive " +
                         "integers.")

    gcd = a[0]
    for i in a[1:]:
        gcd = mathgcd(i, gcd)
        if gcd == 1:
            return 1 

    return gcd

Depending on the use case, it can be faster to omit the sorting step a = np.unique(a).

An alternative (maybe more elegant but slower) implementation using ufuncs is

import numpy as np
from math import gcd as mathgcd
npmathgcd = np.frompyfunc(mathgcd, 2, 1)

def numpy_set_gcd2(a):
    a = np.unique(a)
    if not a.dtype == np.int or a[0] <= 0:
        raise ValueError("Argument must be an array of positive " +
                         "integers.")
    npmathgcd.at(a[1:], np.arange(a.size-1), a[:-1])
    return a[-1]