How to identify if two List are equal regardless of the order?

Question

I have the following 2 objects

List<string> list1
List<string> list2

On list 1 I have 3 items On list 2 I have the same 3 items in a different order.

I need a simple method to return that both lists are equal when they contain the same elements regardless of order

score 19 · Accepted Answer · answered Mar 13 '14 at 22:29

19

You can use SequenceEqual with additional order:

return list1.OrderBy(x => x).SequenceEqual(list2.OrderBy(x => x));

answered Mar 13 '14 at 22:29

MarcinJuraszek

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Selman Genç · Answer 2 · 2014-03-13T22:41:25.637

5

You can use All and Contains method like this, this will return true if both lists contains same elements even if the order is different:

bool control = list1.All(x => list2.Contains(x) && 
                          list1.Count(a => a == x) == list2.Count(b => b == x));

edited Mar 13 '14 at 22:41

answered Mar 13 '14 at 22:28

Selman Genç

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`SequenceEqual` requires items to be in the same order. – MarcinJuraszek Mar 13 '14 at 22:28
ah sorry I didn't see that different order part – Selman Genç Mar 13 '14 at 22:29
`Contains` will return `true` if you have the same item in both list, but different number of times. – MarcinJuraszek Mar 13 '14 at 22:30
then we use `list1.Count == list2.Count` – Selman Genç Mar 13 '14 at 22:31
3

try comparing `{ "1", "2", "2"}` and `{"1", "1", "2"}` now ;) – MarcinJuraszek Mar 13 '14 at 22:31
Well, I don't think it's about me being happy, but yes, your solution should return correct results now. Complexity could be better, but yeah, results are correct. – MarcinJuraszek Mar 13 '14 at 22:44

score 3 · Answer 3 · answered Mar 13 '14 at 22:31

3

Try this:

bool equals = list1.OrderBy(x => x).SequenceEqual(list2.OrderBy(y => y));

I hope this helps ;)

answered Mar 13 '14 at 22:31

Oscar Bralo

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Ray · Answer 4 · 2014-03-13T22:47:17.930

0

You should consider using a HashSet, rather than a List. Its a little less expensive:

HashSet<string> firstSet = new HashSet<string>();
HashSet<string> secondSet = new HashSet<string>();

PopulateSets(firstSet, secondSet); //Example of method you might use to populate your hashsets.

bool isEqual = firstSet.SetEquals(secondSet);

From MSDN:

The SetEquals method ignores duplicate entries and the order of elements in the other parameter.

edited Mar 13 '14 at 22:47

answered Mar 13 '14 at 22:34

Ray

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what if something appeared more than once in the list? – hatchet - done with SOverflow Mar 13 '14 at 22:35
Adding `firstSet` to `HashSet` means you lost information about how many times particular string existed in source collection. – MarcinJuraszek Mar 13 '14 at 22:35
In your example `["a", "a", "b"]` to `["a", "b"]` Which mean that your solution considers only the equality of the unique items, base on the default equality comparer of the type. – Simon Belanger Mar 13 '14 at 22:36
Can you link to more info on `PopulateSets`? – hatchet - done with SOverflow Mar 13 '14 at 22:38
PopulateSets is trivial; It serves to illustrate that you'll need two hashsets, with data in them, in order to do a comparison. – Ray Mar 13 '14 at 22:41

How to identify if two List are equal regardless of the order?

4 Answers4