CODEWITHSUNDEEP
pythonlistfunction
MarcSM23
MarcSM23

Reputation: 21

Efficiently test if two lists have the same elements and length

I got 2 lists:

alist = ['A','B','C','D']
anotherList = ['A','C','B','D']

would like to write a function which returns True if both lists contain the exact same elements, and are same length. I'm kinda new on this stuff, so I got this, which I'm pretty sure it's terrible, and I'm trying to find a more efficient way. Thanks!

def smyFunction(aList,anotherList):
    n = 0
    for element in aList:
        if element in anotherList:
            n = n+1
    if n == len(aList):
        return True
    else:
        return False

Upvotes: 0

Views: 1841

Answers (4)

user2555451
user2555451

Reputation:

Sort the lists with sorted and then compare them with ==:

>>> alist = ['A','B','C','D']
>>> anotherList = ['A','C','B','D']
>>> def smyFunction(aList,anotherList):
...     return sorted(aList) == sorted(anotherList)
...
>>> smyFunction(alist, anotherList)
True
>>>

You need to sort them first in case the elements are out of order:

>>> alist = ['A','B','C','D']
>>> anotherList = ['D','A','C','B']
>>> alist == anotherList
False
>>> sorted(alist) == sorted(anotherList)
True
>>>

Actually, it would probably be better to test the length of the lists first and then use sorted:

return len(alist) == len(anotherList) and sorted(alist) == sorted(anotherList)

That way, we can avoid the sorting operations if the lengths of the list are different to begin with (using len on a list has O(1) (constant) complexity, so it is very cheap).

Upvotes: 1

Hackaholic
Hackaholic

Reputation: 19733

try like this:

def check(a,b):
    return sorted(a) == sorted(b)

Upvotes: 0

Karoly Horvath
Karoly Horvath

Reputation: 96258

If there aren't duplicates, use a set, it doesn't have an order:

set(alist) == set(anotherList)

Upvotes: 0

Cory Kramer
Cory Kramer

Reputation: 117856

The two ways that come to mind are:

1) Use collections.Counter

>>> from collections import Counter
>>> Counter(alist) == Counter(anotherList)
True

2) Compare the sorted lists

>>> sorted(alist) == sorted(anotherList)
True

Upvotes: 4

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