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

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

Answer 2

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

Answer 3

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')

Answer 4

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

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

Answer 5

from pandas import DataFrame
import pandas as pd

d = {'one':[2,3,1,4,5],
     'two':[5,4,3,2,1],
     'letter':['a','a','b','b','c']}

df = pd.DataFrame(d)

#f = lambda x,y: x**2 + y**2
array = []
for i in range(5):
    array.append(df.ix[i,1]**2 + df.ix[i,2]**2)
array = pd.DataFrame(array, columns = ['Sum of Squares'])
test = pd.concat([df,array],axis = 1, join = 'inner')
test = test.sort_index(by = "Sum of Squares", ascending = True).drop('Sum of Squares',axis =1)

Just realized that you wanted this:

    letter  one  two
2      b    1    3
3      b    4    2
1      a    3    4
4      c    5    1
0      a    2    5