DataFrame sorting based on a function of multiple column values

Question

Based on python, sort descending dataframe with pandas:

Given:

from pandas import DataFrame
import pandas as pd

d = {\'x\':[2,3,1,4,5],
     \'y\':[         


        

Answer 1

Another approach, similar to this one is to use argsort which returns the indexes permutation directly:

f = lambda r: r.x**2 + r.y**2
df.iloc[df.apply(f, axis=1).argsort()]

I think using argsort better translates the idea than a regular sort (we don't care about the value of this computation, only about the resulting indexes).

It could also be interesting to patch the DataFrame to add this functionality:

def apply_sort(self, *, key):
    return self.iloc[self.apply(key, axis=1).argsort()]

pd.DataFrame.apply_sort = apply_sort

We can then simply write:

>>> df.apply_sort(key=f)

   x  y letter
2  1  3      b
3  4  2      b
1  3  4      a
4  5  1      c
0  2  5      a