Test if two lists of lists are equal

Question

Say I have two lists of lists in Python,

l1 = [['a',1], ['b',2], ['c',3]]
l2 = [['b',2], ['c',3], ['a',1]]

What is the most elegant way to test they are equal in the sense that the elements of l1 are simply some permutation of the elements in l2?

Note to do this for ordinary lists see here, however this uses set which does not work for lists of lists.

Are the inner lists considered "equal" if one is a permutation of another? In both cases, what about repetitions? — Kyle Strand
– Kyle Strand, Commented Dec 22, 2014 at 15:53

Kevin · Accepted Answer · 2014-12-22 15:43:50Z

16

l1 = [['a',1], ['b',2], ['c',3]]
l2 = [['b',2], ['c',3], ['a',1]]
print sorted(l1) == sorted(l2)

Result:

True

answered Dec 22, 2014 at 15:43

Kevin

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Comments

Irshad Bhat · Accepted Answer · 2014-12-22 15:48:39Z

3

Set doesn't work for list of lists but it works for list of tuples. Sou you can map each sublist to tuple and use set as:

>>> l1 = [['a',1], ['b',2], ['c',3]]
>>> l2 = [['b',2], ['c',3], ['a',1]]
>>> print set(map(tuple,l1)) == set(map(tuple,l2))
True

answered Dec 22, 2014 at 15:48

Irshad Bhat

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2 Comments

DSM Over a year ago

This would lose information about the count: in other words, if l1 had 10 ['a', 1] sublists and l2 only had 1, it would still say they're equal. (Maybe that's what the OP wants, but it's not what I'd guessed based on "permutation".)

Òscar Raya Over a year ago

It might not be what OP wanted but this is what I actually needed searching with this question as in my case I did not have repetions and the lists inside weren't ordered.

Community · Accepted Answer · 2017-05-23 10:32:41Z

1

For one liner solution to the above question, refer to my answer in this question

I am quoting the same answer over here. This will work regardless of whether your input is a simple list or a nested one.

let the two lists be list1 and list2, and your requirement is to ensure whether two lists have the same elements, then as per me, following will be the best approach :-
if ((len(list1) == len(list2)) and
   (all(i in list2 for i in list1))):
    print 'True'
else:
    print 'False'
The above piece of code will work per your need i.e. whether all the elements of list1 are in list2 and vice-verse. Elements in both the lists need not to be in the same order.

But if you want to just check whether all elements of list1 are present in list2 or not, then you need to use the below code piece only :-
if all(i in list2 for i in list1):
    print 'True'
else:
    print 'False'
The difference is, the later will print True, if list2 contains some extra elements along with all the elements of list1. In simple words, it will ensure that all the elements of list1 should be present in list2, regardless of whether list2 has some extra elements or not.

edited May 23, 2017 at 10:32

CommunityBot

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answered Jan 22, 2015 at 12:55

Pabitra Pati

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1 Comment

Manoj Over a year ago

exactly what i have been looking for

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