DataFrame sorting based on a function of multiple column values

Have you tried to create a new column and then sorting on that. I cannot comment on the original post, so i am just posting my solution.

df['c'] = df.a**2 + df.b**2
df = df.sort_values('c')

df.loc[(df.x ** 2 + df.y ** 2).sort_values().index]

after How to sort pandas dataframe by custom order on string index

You can create a temporary column to use in sort and then drop it:

df.assign(f = df['one']**2 + df['two']**2).sort_values('f').drop('f', axis=1)
Out: 
  letter  one  two
2      b    1    3
3      b    4    2
1      a    3    4
4      c    5    1
0      a    2    5