python sort method 에 대해 알아보자 (feat. python Sorting HOW TO)
June 22,2020
, 5 min read
sort 그냥 하면 되는거 아니야!?
그냥 하면 당연히 잘 동작한다.(!?) 하지만 객체로 다뤄야 하는 sort then sort 방법, 객체가 담고있는 변수기반 sort 방법 등은 익혀두어야 한다.
python Tutorial 을 보자
기본적인 사용법
a = [5, 2, 3, 1, 4]
s_a = sorted(a)
re_s_a = sorted(a,reverse=True)
print(a) # [5, 2, 3, 1, 4]
print(s_a) # [1, 2, 3, 4, 5]
print(re_s_a) # [5, 4, 3, 2, 1]
print(sorted(a)) # [1, 2, 3, 4, 5]Key functions
key 를 사용하면 비교를 위한 전처리를 진행할 수 있다.
print(sorted("This is a test string from Andrew".split()))
print(sorted("This is a test string from Andrew".split(), key=str.lower))
# ['Andrew', 'This', 'a', 'from', 'is', 'string', 'test']
# ['a', 'Andrew', 'from', 'is', 'string', 'test', 'This']
print(sorted("90 30 40 50 60 10 20 101".split())) # 단순 str
print(sorted("90 30 40 50 60 10 20 101".split(), key=int))
# ['10', '101', '20', '30', '40', '50', '60', '90']
# ['10', '20', '30', '40', '50', '60', '90', '101']sort two fields
튜플도 잘 sorting 한다. 두개 이상의 sorting 도 가능하다.
student_tuples = [
('john', 'A', 15),
('jane', 'B', 12),
('dave', 'B', 10),
]
print(sorted(student_tuples, key=lambda student: student[2]))
# [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
print(sorted(student_tuples, key=lambda student: (student[1],student[2]))) # [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]objects 의 attributes 로도 잘 동작한다.
class Student:
def __init__(self, name, grade, age):
self.name = name
self.grade = grade
self.age = age
def __repr__(self):
return repr((self.name, self.grade, self.age))
student_objects = [
Student('john', 'A', 15),
Student('jane', 'B', 12),
Student('dave', 'B', 10),
]
print(sorted(student_objects, key=lambda student: student.age))
# [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
student_objects = [
Student('john', 'A', 15),
Student('jane', 'B', 12),
Student('Bdave', 'B', 10),
Student('Adave', 'A', 10),
Student('Cdave', 'C', 10),
]
print(sorted(student_objects, key=lambda student: (student.age,student.grade)))# [('Adave', 'A', 10), ('Bdave', 'B', 10), ('Cdave', 'C', 10), ('jane', 'B', 12), ('john', 'A', 15)]operator 모듈의 itemgetter로 attrgetter 로 접근하여 동작시킬 수 있다.
*itemgetter
After f = itemgetter(2), the call f(r) returns r[2].
After g = itemgetter(2, 5, 3), the call g(r) returns (r[2], r[5], r[3]).
*attrgetter
After f = attrgetter('name'), the call f(b) returns b.name.
After f = attrgetter('name', 'date'), the call f(b) returns (b.name, b.date).
After f = attrgetter('name.first', 'name.last'), the call f(b) returns (b.name.first, b.name.last).
from operator import itemgetter, attrgetter
class Student:
def __init__(self, name, grade, age):
self.name = name
self.grade = grade
self.age = age
def __repr__(self):
return repr((self.name, self.grade, self.age))
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),
]
print(sorted(student_tuples, key=itemgetter(2)))
print(sorted(student_objects, key=attrgetter('age')))
# [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
# [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
# Sorting two fields
print(sorted(student_tuples, key=itemgetter(1,2)))
print(sorted(student_objects, key=attrgetter('grade', 'age')))
# [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]
# [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]Sorts are guaranteed to be stable.
stable sort 이다.
즉, Key 가 아닌것 끼리는 앞 뒤가 변경되지 않는다!
data = [('red', 1), ('blue', 2), ('red', 2), ('blue', 1)]
print(sorted(data, key=itemgetter(0)))
# [('blue', 2), ('blue', 1), ('red', 1), ('red', 2)]
print(sorted(data, key=itemgetter(0),reverse=True))
# [('red', 1), ('red', 2), ('blue', 2), ('blue', 1)]
print(sorted(data, key=itemgetter(1)))
# [('red', 1), ('blue', 1), ('blue', 2), ('red', 2)]
print(sorted(data, key=itemgetter(1),reverse=True))
# [('blue', 2), ('red', 2), ('red', 1), ('blue', 1)]그러니 단순한 sort 두번으로 two fields sort가 가능하다.
from operator import itemgetter, attrgetter
class Student:
def __init__(self, name, grade, age):
self.name = name
self.grade = grade
self.age = age
def __repr__(self):
return repr((self.name, self.grade, self.age))
student_objects = [
Student('john', 'A', 15),
Student('jane', 'B', 12),
Student('Bdave', 'B', 10),
Student('Adave', 'A', 10),
Student('Cdave', 'C', 10),
]
print(sorted(student_objects, key=lambda student: (student.age,student.grade)))# [('Adave', 'A', 10), ('Bdave', 'B', 10), ('Cdave', 'C', 10), ('jane', 'B', 12), ('john', 'A', 15)]
s = sorted(student_objects, key=attrgetter('grade')) # sort on secondary keyprint(sorted(s, key=attrgetter('age')))# [('Adave', 'A', 10), ('Bdave', 'B', 10), ('Cdave', 'C', 10), ('jane', 'B', 12), ('john', 'A', 15)]복잡한 sort
여러 필드를 sort 해야할때, 특정한 필드에 대해서는 reverse를 적용해야한다면, 단순한 two fields 방식으로 sort 가 안된다.
방금 위의 두번의 sort 방식은 순서를 거꾸로 진행해야 되니, 실수 할 가능성이 크다. 아래의 multisort 처럼 구현하여, two fields 처럼 사용하자.
from operator import itemgetter, attrgetter
class Student:
def __init__(self, name, grade, age):
self.name = name
self.grade = grade
self.age = age
def __repr__(self):
return repr((self.name, self.grade, self.age))
student_objects = [
Student('john', 'A', 15),
Student('jane', 'B', 12),
Student('Bdave', 'B', 10),
Student('Adave', 'A', 10),
Student('Cdave', 'C', 10),
]
# for key, reverse in reversed(specs) 이므로 two fields 처럼 동작한다.
def multisort(xs, specs):
for key, reverse in reversed(specs):
xs.sort(key=attrgetter(key), reverse=reverse)
return xs
print(multisort(list(student_objects), (('grade', False), ('age', True))))
# [('john', 'A', 15), ('Adave', 'A', 10), ('jane', 'B', 12), ('Bdave', 'B', 10), ('Cdave', 'C', 10)]
print(multisort(list(student_objects), (('grade', False), ('age', False))))
# [('Adave', 'A', 10), ('john', 'A', 15), ('Bdave', 'B', 10), ('jane', 'B', 12), ('Cdave', 'C', 10)]