how to sort a list that is contained in an object

Question

The task is to code a sorting algorithm using the below code as a starting point. The issue is I cannot seem to figure out how I go about starting the code, I'm not looking for the full solution - just techniques in how to sort lists of tuples that are actually part of an object. I get errors when I try to iterate through the list, saying cannot iterate through an object.

class LinkedList:
    def __init__(self, data):
        self.label = data[0][0]
        self.value = data[0][1]
        self.tail = None if (len(data) == 1) else LinkedList(data[1:])

countries = LinkedList([("Ukraine",41879904),("Brunei",442400),("Christmas Island (Australia)",1928)

I get errors when I try to iterate through the list saying can not iterate through an object Show us. — John Gordon
– John Gordon, Commented Jun 4, 2020 at 15:34
'for x in countries: for y in x: print(countries)' Traceback (most recent call last): File "C:/Users/cheet/.PyCharmCE2019.3/config/scratches/scratch_2.py", line 11, in <module> for x in countries: TypeError: 'LinkedList' object is not iterable — NateD0gg83
– NateD0gg83, Commented Jun 4, 2020 at 15:38

Vorashil Farzaliyev · Accepted Answer · 2020-06-04 15:45:38Z

1

You can use a pointer to iterate through linked list.:

curr = countries

while curr:
    print("Label {}, Value {}".format(curr.label, curr.value))
    curr = curr.tail

In order to sort linked list, firstly, you need to implement helper functions to remove/insert a node to given linked list at certain position. Once you have such methods, you can implement any of the famous sorting algorithms (e.g quick sort) using your helper methods you just created.

answered Jun 4, 2020 at 15:45

Vorashil Farzaliyev

4545 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Aziz Sonawalla · Accepted Answer · 2020-06-04 15:39:05Z

0

To iterate over this list you need to keep getting the tail reference of the object:

class LinkedList:
  def __init__(self, data):
    self.label = data[0][0]
    self.value = data[0][1]
    self.tail = None if (len(data) == 1) else LinkedList(data[1:])

countries = LinkedList([("Ukraine",41879904),("Brunei",442400),("Christmas Island (Australia)",1928)])
nextObj = countries

while nextObj is not None:
  print(nextObj.label, nextObj.value)
  nextObj = nextObj.tail

print("done!")

output:

Ukraine 41879904
Brunei 442400
Christmas Island (Australia) 1928
done!

To get an element at a certain index, you start iterating from the first element and just keep a counter.

answered Jun 4, 2020 at 15:39

Aziz Sonawalla

2,5121 gold badge7 silver badges6 bronze badges

Comments

AdamF · Accepted Answer · 2020-06-04 15:57:23Z

functools, @total_ordering

One of the powerful features in python. you can sort objects in a classic and easy straitforward way. Functools module in python helps in implementing higher-order functions. Higher-order functions are dependent functions that call other functions. Total_ordering provides rich class comparison methods that help in comparing classes without explicitly defining a function for it. So, It helps in the redundancy of code.

There are 2 essential conditions to implement these comparison methods

At least one of the comparison methods must be defined from lt(less than), le(less than or equal to), gt(greater than) or ge(greater than or equal to).

The eq function must also be defined

from functools import total_ordering

@total_ordering
class LinkedList(object):
    def __init__(self, data):
        self.label = data[0][0]
        self.value = data[0][1]

    def __lt__(self, other):
        return self.label < other.value  ##lets assume that the sort is based on label data member(attribute)

    def __eq__(self, other):
        return self.label == other.value

##I dont know what data is. just pass your data objects to list of LinkedList objects. and sort it with sorted method (treat them like int objects)! 
my_list = [LinkedList(data0),LinkedList(data1),LinkedList(data2)]

new_list=my_list.sorted()
for obj in new_list:
    print(...)

Collectives™ on Stack Overflow

how to sort a list that is contained in an object

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related