Counting Objects in a List according to a Boolean property

Question

I have a list of objects with a boolean property.

I'd like to count these objects according to this boolean property - None's included.

Are there functions in the standard library that would be more efficient, terser, or more Pythonic than fully writing out a loop to iterate over them?

Counter does not seem appropriate, and this nor this solve the problem - as far as I can tell.

class MyObject():
    def __init__(self, moniker, booleanVariable):
        self.name = moniker
        self.state = booleanVariable

def _myCounterMethod(list):
    # code goes here
    return counts

myList = []
myList.append(MyObject("objectOne", True))
myList.append(MyObject("objectTwo", False))
myList.append(MyObject("objectThree", None))

counts = _MyCounterMethod(myList)
print(counts)
>>>[('True', 1), ('False', 1), ('None', 1)]

My current solution:

def _myCounterMethod(list):
    trueCount = 0
    falseCount = 0
    noneCount = 0
    for obj in list:
        if obj.state == True:
            trueCount += 1
        elif obj.state == False:
            falseCount += 1
        elif obj.state == None:
            noneCount += 1
    countsList = [('True', trueCount), ('False', falseCount), ('None', noneCount)]
    return countsList

user2390182 · Answer 1 · 2021-10-11T16:33:03.180

You are already covered with Counter based approaches, here is a simple shortening of what you have:

def _myCounterMethod(lst):  # do not shadow `list`
    trueCount = falseCount = noneCount = 0
    for obj in lst:
        trueCount += obj.state is True
        falseCount += obj.state is False
        noneCount += obj.state is None
    return [('True', trueCount), ('False', falseCount), ('None', noneCount)]

And for my take on the best approach:

from collections import Counter
from operator import attrgetter

def _myCounterMethod(lst):
    return Counter(map(attrgetter("state"), lst)).most_common()
    # already a list of tuples

Convert whatever you have to strings only when you are printing it really and really need to.

May or may not be what is desired, but it's already a list and since it is destined for output, descending sort order can only be a plus :-) — user2390182, Oct 11 '21 at 16:21

Dani Mesejo · Accepted Answer · 2021-10-11T16:12:44.327

1

Use collections.Counter:

import collections


class MyObject():
    def __init__(self, moniker, booleanVariable):
        self.name = moniker
        self.state = booleanVariable


my_list = [MyObject("objectOne", True), MyObject("objectTwo", False), MyObject("objectThree", None)]

counts = collections.Counter(str(e.state) for e in my_list)
print(counts)

Output

Counter({'True': 1, 'False': 1, 'None': 1})

If strictly list output is needed do:

result = list(counts.items())
print(result)

Output

[('True', 1), ('False', 1), ('None', 1)]

edited Oct 11 '21 at 16:12

answered Oct 11 '21 at 16:04

Dani Mesejo

61,499
6
49
76

@schwobaseggl It's not a hard requirement, but the end utility _is_ printing state to the console - so it would be convenient. – farAndAway Oct 11 '21 at 16:12

score 1 · Answer 3 · answered Oct 11 '21 at 16:06

1

I suggest you implement the .count() method

def counter(l):
   iter = [x.state for x in l]
   return ('True', iter.count(True)), ('False', iter.count(False)), ('None', iter.count(None))

>>> counter(myList)
(('True', 1), ('False', 1), ('None', 1))

answered Oct 11 '21 at 16:06

Alexandre Mahdhaoui

801
5
10

According to [this question](https://stackoverflow.com/questions/44812468/what-is-the-time-complexity-of-python-lists-count-function), count makes use of a loop that iterates over the entire list to find the value of the provided field. So while this is quite readable, you are iterating over the list's length 4 times in total – farAndAway Oct 11 '21 at 16:31

score 0 · Answer 4 · answered Oct 11 '21 at 16:05

The below seems to work

from collections import defaultdict

data = defaultdict(int)
class MyObject():
    def __init__(self, moniker, booleanVariable):
        self.name = moniker
        self.state = booleanVariable
myList = []
myList.append(MyObject("objectOne", True))
myList.append(MyObject("objectTwo", False))
myList.append(MyObject("objectThree", None))
for o in myList:
  data[str(o.state)] += 1
print(data)

output

defaultdict(<class 'int'>, {'True': 1, 'False': 1, 'None': 1})

Counting Objects in a List according to a Boolean property

4 Answers4