使用文本文件中的信息对列表进行排序

Question

I have been reading class objects from a text file and stored the information in a list. My question is: How can I sort the list in a numerical order.

Text file:

Hugo 10
Isac 9
John 90
Kelly 8

Code:

class A:
    def __init__(self,name, age):
        self.name = name
        self.age = age

def sort_list():  
    a = list()        
    file = open('my_textfile.txt', 'r').readlines()       
    for k in file:
        k = k.split(' ')
        af = A(k[0], k[1])
        a.append(af)       
    return a

Then I want to sort my list so that both columns get sorted numerically. Like this:

Kelly 8
Isac 9
Hugo 10
John 90

Answer 1

Here is one solution using the code you suggest. Break the data into two parts sort it and put it back together again. There are other ways of doing this with pandas.

class A:
    def __init__(self,name, age):
        self.name = name
        self.age = age
def sort_list():  
    a = list()        
    name = list()
    data = list()
    file = open('my_textfile.txt', 'r').readlines()       
    for k in file:
        k = k.split(' ')
        name.append(k[0])
        data.append(k[1])
    name.sort()
    data.sort()
    length = len(name)
    for i in range(length):
        af = A(name[i], data[i])
        a.append(af)
    return a

Answer 2

You most likely have found a solution now. If not, let me suggest something.

First, I made a slight modification to your class: I added a string representation that makes prints more readable:

class A:

    def __repr__(self):
        return f"A('{self.name}', {self.age})"

    def __init__(self, name, age):
        self.name = name
        self.age = age

You don't need that for the following!

Now the sorting:

def sort_list():
    lst = list()
    lines = open('my_textfile.txt', 'r').readlines()
    for line in lines:
        line = line.split()
        lst.append(A(line[0], int(line[1])))
    lst.sort(key=lambda a: (a.age, a.name))
    return lst

Apart from renaming some variables I have made the following adjustments:

• I converted the second part of the strings to an int because I think that's what you actually want ( int(line[1]) ).
• After appending all the data to the list it get's sorted. Lists have a sort method, but in your case you have to give it some hints on how to sort, since the elements are a new class. The hint is the lambda function given to the optional key argument of sort . It returns for every element of the list the tuple (a.age, a.name) . sort then actually sorts according to this values. Since the age is first, the sorting looks a it first and the result is an increasing age in the final list. For entries with same age the sorting proceeds in alphabetical order on the names.

The result of

lst = sort_list()
print(lst)

is

[A('Kelly', 8), A('Isac', 9), A('Hugo', 10), A('John', 90)]