How do I perform secondary sorting in python?

Question

If i have a list of numbers [4,2,5,1,3]
I want to sort it first by some function f and then for numbers with the same value of f i want it to be sorted by the magnitude of the number.

This code does not seem to be working.

list5 = sorted(list5)
list5 = sorted(list5, key = lambda vertex: degree(vertex))

Secondary sorting first: list5 is sorted based on magnitude.
Primary sorting next: list5 is sorted based on some function of the numbers.

Asked By: Vinu K S

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Source

Answer 1

Sort it by a (firstkey, secondkey) tuple:

sorted(list5, key=lambda vertex: (degree(vertex), vertex))

Answered By: Pavel Anossov

Answer 2

On a phone, but youcan sort by tuple.

sorted(list5, lambda x: (degree(x),x))

Don’t forget the reverse flag if you need it.

Answered By: jay3686

Answer 3

From the Python 3 docs on sorting

from operator import itemgetter, attrgetter
student_objects = [
    Student('john', 'A', 15),
    Student('jane', 'B', 12),
    Student('dave', 'B', 10),
]
student_tuples = [
    ('john', 'A', 15),
    ('jane', 'B', 12),
    ('dave', 'B', 10),
]

#The operator module functions allow multiple levels of sorting. For example, to sort by grade then by age:

sorted(student_tuples, key=itemgetter(1,2))
sorted(student_objects, key=attrgetter('grade', 'age'))

Answered By: claudio

Answer 4

This is how I would do.

s = ['a', 'ac', 'b', 'ab']
s.sort(key=lambda x: (x[0], x[1]) if len(x)>1 else (x[0],))

Result:

['a', 'ab', 'ac', 'b']

Answered By: Anish

How do I perform secondary sorting in python?

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