LINQ: check whether two list are the same

Question

This should be easy.

I want to check whether two list are the same in that they contain all the same elements or not, orders not important.

Duplicated elements are considered equal, i.e.e, new[]{1,2,2} is the same with new[]{2,1}

@280Z28: so you voted down a question because of the answers? Doesn't sound very reasonable. — Graviton, Oct 27 '09 at 06:15
The SetEquals of HashSet is best suited for checking whether two sets are equal as defined in this question — LCJ, Dec 02 '12 at 09:25

leppie · Accepted Answer · 2009-10-27T04:53:46.453

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var same = list1.Except(list2).Count() == 0 && 
           list2.Except(list1).Count() == 0;

edited Oct 27 '09 at 04:53

answered Oct 27 '09 at 04:29

leppie

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What is a differing duplicate? – leppie Oct 27 '09 at 06:00
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An even more "linq-ish" version: `!list1.Except(list2).Any() && !list2.Except(list1).Any()` – TLS Jan 13 '12 at 21:08
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@TLS And it doesn't require counting all of the differences, just the first. – Samantha Branham Jul 14 '15 at 17:47

Sam Harwell · Answer 2 · 2009-10-27T06:19:51.173

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Edit: This was written before the OP added that { 1, 2, 2 } equals { 1, 1, 2 } (regarding handling of duplicate entries).

This will work as long as the elements are comparable for order.

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

edited Oct 27 '09 at 06:19

answered Oct 27 '09 at 04:28

Sam Harwell

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This wont help with duplicates. – leppie Oct 27 '09 at 04:29
@leppie: What do you mean? If `list1` contains 4 `3`, then `equal` would only be true if `list2` also contained exactly 4 `3`. Duplicates work fine. – Sam Harwell Oct 27 '09 at 04:33
You can take out the OrderBy calls if the order of the sequence will be the same; such as when you are comparing occurrence lists from tests. – Jason Oct 27 '09 at 04:35
@Jason: True, but the question explicitly states that you can't assume anything about the order of the elements. – Sam Harwell Oct 27 '09 at 04:36
And what about 3 elements vs 10 elements, all elements being 'a'. – leppie Oct 27 '09 at 04:55
@leppie: Then obviously the lists are not the same, and it returns the correct answer: false. – Sam Harwell Oct 27 '09 at 04:56
But they contain all the same elements, like the OP asked. – leppie Oct 27 '09 at 06:01
if you add a ".Distinct()" to list1 and list2, this will also handle duplicates and return the correct answer as the question desires. – ThisGuy Dec 22 '13 at 06:12

score 4 · Answer 3 · edited May 23 '17 at 12:00

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The SetEquals of HashSet is best suited for checking whether two sets are equal as defined in this question

        string stringA = "1,2,2";
        string stringB = "2,1";

        HashSet<string> setA = new HashSet<string>((stringA.Trim()).Split(',').Select(t => t.Trim()));
        HashSet<string> setB = new HashSet<string>((stringB.Trim()).Split(',').Select(t => t.Trim()));

        bool isSetsEqual = setA.SetEquals(setB);

REFERENCE:

Check whether two comma separated strings are equal (for Content set)

edited May 23 '17 at 12:00

Community

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answered Dec 02 '12 at 09:22

LCJ

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Using HashSets seems like the most elegant way to do this (and probably pretty fast too.) – ThisGuy Dec 22 '13 at 06:14
Only if you rely on hash to be unique. I guess that with the right hash it will be unique for the numbers it can represent - but then it shouldn't be faster. – LosManos Oct 17 '22 at 05:09

jrista · Answer 4 · 2009-10-27T05:25:24.123

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You need to get the intersection of the two lists:

bool areIntersected = t1.Intersect(t2).Count() > 0;

In response to you're modified question:

bool areSameIntersection = t1.Except(t2).Count() == 0 && t2.Except(t1).Count() == 0;

edited Oct 27 '09 at 05:25

answered Oct 27 '09 at 03:48

jrista

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I think my question is not phrased clearly... I've modified the question – Graviton Oct 27 '09 at 03:54
If `t1` is { 1, 2, 2 } and `t2` is { 1, 2, 2 }, this will incorrectly return false. – Sam Harwell Oct 27 '09 at 04:42

LINQ: check whether two list are the same

4 Answers4