CODEWITHSUNDEEP
python
Joelbitar
Joelbitar

Reputation: 3605

What is the best way to sort items on one of the items values

I have two instances of an object in a list

class Thing():
     timeTo = 0
     timeFrom = 0
     name = ""

o1 = Thing()
o1.name = "One"
o1.timeFrom = 2

o2 = Thing()
o2.timeTo = 20
o2.name = "Two"

myList = [o1, o2]


biggestIndex = (myList[0].timeFrom < myList[1].timeTo) & 1
bigger  = myList.pop(biggestIndex)
lesser  = myList.pop()

print bigger.name
print lesser.name

both o1 and o2 have two properties that I want to compare the first in the lists timeFrom property and the second ones timeTo property to eachother.

I feel this is a bit awkward and wierd, is there perhaps a better and more readable approach to this?

Upvotes: 2

Views: 206

Answers (3)

dugres
dugres

Reputation: 13085

see attrgetter

import operator

getter = operator.attrgetter('timeFrom')

bigger = max(myList, key=getter)  
lesser = min(myList, key=getter)

print bigger.name  
print lesser.name

EDIT :

attrgetter also wokrs with sorted or anywhere a key function is needed.

lesser, bigger = sorted(myList, key=getter)

Upvotes: 1

Tony Veijalainen
Tony Veijalainen

Reputation: 5555

I would do this, if object can have only one of the time values:

class Thing(object):
    def __init__(self, name, time = 0, timename = 'to'):
        self.name, self.time, self.timename = (name,time,timename)

    def __repr__(self):
        return "Thing(%r, %i, %r)" % (self.name, self.time, self.timename)

    def __lt__(self, other):
        return self.time < other.time

o1 = Thing("One", 5, 'from')

o2 = Thing("Two", 20, 'to')

myList = [o1, o2]

print myList
print max(myList)
print min(myList)

Upvotes: 0

Jochen Ritzel
Jochen Ritzel

Reputation: 107608

The best solution is to make Thing instances sortable. You do this by implementing __lt__:

class Thing():
     timeTo = 0
     timeFrom = 0
     name = ""

     def __lt__(self, other):
         return self.timeFrom < other.timeTo


lesser, bigger = sorted(myList)

Python2 has lesser, bigger = sorted(myList, cmp=lambda one,other: one.timeFrom < other.timeTo).

In Python3 cmp is gone, I guess to force people to do (or learn) OOP and write a adapter.

class SortAdaper(object):
    def __init__(self, obj ):
        self.obj = obj

class TimeLineSorter(SortAdaper):
    """ sorts in a timeline """
    def __lt__(self, other):
        return self.obj.timeFrom < other.obj.timeTo

class NameSorter(SortAdaper):
    """ sorts by name """
    def __lt__(self, other):
        return self.obj.name < other.obj.name

print sorted( myList, key=TimeLineSorter)
print sorted( myList, key=NameSorter)

Upvotes: 2

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