Detailed explanation of python3 list sorting function

ztenv 2020-11-13 13:00:03
detailed explanation python3 python list


Python3 list Sort function details

One 、            List sort Sorting function

The function prototype :

         list.sort(key=None,reverse=False)

The functionality :

Sort the original list , After sorting , The original list becomes an ordered list . By default ( When no parameters are passed in ) Sort in dictionary order .

Function parameter :

(1)     key: It's basically a comparison element , There is only one parameter , The parameters of the specific function are taken from the iterable object . Specifies an element in an iteratable object to sort. Specifies a single element or multiple elements to use when sorting 、lambda expression ;

(2)     reverse: Refers to whether the word sorting rule is ascending or descending , Sort ascending by default ;

Two 、            Examples of sorting

1.       String sort

def list_sort_string():
list=["delphi","Delphi","python","Python","c++","C++","c","C","golang","Golang"]
list.sort() # In ascending dictionary order
print(" Ascending :",list)
list.sort(reverse=True) # Sort in descending order
print(" Descending :",list)

 

Sorting result :

 

 Ascending : ['C', 'C++', 'Delphi', 'Golang', 'Python', 'c', 'c++', 'delphi', 'golang', 'python']
Descending : ['python', 'golang', 'delphi', 'c++', 'c', 'Python', 'Golang', 'Delphi', 'C++', 'C']

2.       Numerical sort

def list_sort_number():
list=[30,40,10,50,50.1,80,60,100,90]
list.sort()
print(" Ascending :",list)
list.sort(reverse=True)
print(" Descending :",list)

Sorting result :

 Ascending : [10, 30, 40, 50, 50.1, 60, 80, 90, 100]
Descending : [100, 90, 80, 60, 50.1, 50, 40, 30, 10]

 

3.       Sort according to the properties of class objects in the list

 

class element(object):
def __init__(self,id="",name=""):
self.id=id
self.name=name
def __lt__(self, other): # override < The operator
if self.id<other.id:
return True
return False
def __str__(self): # override __str__
return "id={0},name={1}".format(self.id,self.name)
def sort_by_attribute():
list=[element(id="130",name="json"),
element(id="01",name="jack"),element(id="120",name="tom")]
list.sort()
for item in list:
print(item)

 

because list.sort() Function when sorting , Using less than sign contrast , So custom data types need override __lt__( Less than ) Function to achieve sorting .

 

according to element Of id Property sort

Sort the result of the column :

id=01,name=jack
id=120,name=tom
id=130,name=json

4.       Sort by the length of the elements in the list

def list_sort_by_length():
list=["delphi","Delphi","python","Python","c++","C++","c","C","golang","Golang"]
list.sort(key=lambda ele:len(ele)) # In ascending order of element length
print(" Ascending :",list)
list.sort(key=lambda ele:len(ele),reverse=True) # Sort in descending order
print(" Descending :",list)

 

With the help of lambda expression , Calculation list The length of the elements in the list , Sort by the length of the elements

 

Results of sorting :

 Ascending : ['c', 'C', 'c++', 'C++', 'delphi', 'Delphi', 'python', 'Python', 'golang', 'Golang']
Descending : ['delphi', 'Delphi', 'python', 'Python', 'golang', 'Golang', 'c++', 'C++', 'c', 'C']

 

5.       Sort by multiple attributes of elements in the list :

 

def two_d_list_sort():
list=[ ["1","c++","demo"],
["1","c","test"],
["2","java",""],
["8","golang","google"],
["4","python","gil"],
["5","swift","apple"]
]
list.sort(key=lambda ele:ele[0])# According to the first 1 Order of elements
print(list)
list.sort(key=lambda ele:ele[1]) # First, according to the 2 Order of elements
print(list)
list.sort(key=lambda ele:(ele[1],ele[0])) # First, according to the 2 Order of elements , And then according to 1 Order of elements
print(list)

 

By the same token lambda Expression complete , Of course, you can also define a relationship with labmda Functions with the same meaning realize sorting .

 

Sorting result :

[['1', 'c++', 'demo'], ['1', 'c', 'test'], ['2', 'java', ''], ['4', 'python', 'gil'], ['5', 'swift', 'apple'], ['8', 'golang', 'google']]
[['1', 'c', 'test'], ['1', 'c++', 'demo'], ['8', 'golang', 'google'], ['2', 'java', ''], ['4', 'python', 'gil'], ['5', 'swift', 'apple']]
[['1', 'c++', 'demo'], ['1', 'c', 'test'], ['8', 'golang', 'google'], ['2', 'java', ''], ['4', 'python', 'gil'], ['5', 'swift', 'apple']]

 

6.       Dynamically sort according to the user specified index

 

occasionally , Before you write the code , I don't know which columns to sort according to the two-dimensional table , It's based on input or configuration when the program is running , In order to solve the problem of dynamic sorting by multiple columns or attributes , With the help of eval() function ,eval Function can compile a string into python Code and run , So as to achieve dynamic sorting according to multiple columns or attributes .

Sorting result :

 Sort index : 0 [['1', 'c++', 'demo'], ['1', 'c', 'test'], ['2', 'java', ''], ['4', 'python', 'gil'], ['5', 'swift', 'apple'], ['8', 'golang', 'google']]
Sort index : 1 [['1', 'c', 'test'], ['1', 'c++', 'demo'], ['8', 'golang', 'google'], ['2', 'java', ''], ['4', 'python', 'gil'], ['5', 'swift', 'apple']]
Sort index : 2 [['2', 'java', ''], ['5', 'swift', 'apple'], ['1', 'c++', 'demo'], ['4', 'python', 'gil'], ['8', 'golang', 'google'], ['1', 'c', 'test']]
Sort index : 1,0 [['1', 'c++', 'demo'], ['1', 'c', 'test'], ['8', 'golang', 'google'], ['2', 'java', ''], ['4', 'python', 'gil'], ['5', 'swift', 'apple']]

 

Sum up , It basically sums up list.sort Most of the scenarios used by , as follows :

 

1、 Default sort

2、 Sort according to a single attribute of a class object , Of course, it can also be extended to sort according to multiple attributes of class objects

3、 Sort the elements according to their intrinsic properties , Such as : length 、 The first N Elements, etc . For simplicity , So with the help of lambda expression , Of course, you can use ordinary functions instead of lambda expression

4、 Dynamic sorting by multiple columns , At the same time with the help of lambda and eval() Function implementation

5、 In addition, compared with Python2,Python3 To cancel the sort Function  cmp The way , Only use key The way .
      therefore python2 use cmp The functions written in this way are migrated to python3 You need to convert .
     from functools import cmp_to_key

    sort(iterable, key=cmp_to_key(cmp_fun))

   < thank CSDN:xpresslink Correction >

There may be other scenarios that don't involve , But I believe , The above conditions can satisfy 90% The above scene ; If you have any problem in use, please leave a message .

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