I want to sort the following DataFrame on the b-column first and then the a-column.

The math.isclose() function should be used to compare the floats in the b-column. Therefore, I wrote a custom compare function and use the cmp_to_key function from functools. However, when sorting the data frame I get the following error:

TypeError: object of type ‘functools.KeyWrapper’ has no len()

Here’s my full code:

import pandas as pd
from functools import cmp_to_key
from math import isclose
import numpy as np

my_list = [
[0, 1.2],
[2, 0.07076863960397785],
[1, 0.07076863960397783],
[4, 0.02],
[3, 0.07076863960397784]
]

df = pd.DataFrame(my_list,columns=['a','b'])

def compare(a,b):
  if isclose(a,b):
    return 0
  elif a-b<0:
    return -1
  else:
    return 1

df.sort_values(by=['b','a'],key= cmp_to_key(compare))

Now, I know the key in sort_values expects a series, so the key function should be vectorized. But I don’t know how to accomplish this.

This should be the final result: