What is the shortest way to compare if two IEnumerable<T> have the same items in C#? [duplicate]

This question already has answers here: Closed 12 years ago.

Possible Duplicate:

Test whether two IEnumerable<T> have the same values with the same frequencies

I wrote

UPDATED - correction:

static bool HaveSameItems<T>(this IEnumerable<T> self, IEnumerable<T> other)
{
    return ! 
    ( 
        other.Except(this).Any() ||
        this.Exce开发者_如何学JAVApt(other).Any()
    );
}

Isn't there a shorter way? I know there is SequenceEqual but the order doesn't matter for me.

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Even if the order doesn't matter to you, it doesn't rule out SequenceEqual as a viable option.

var lst1 = new [] { 2,2,2,2 };
var lst2 = new [] { 2,3,4,5 };
var lst3 = new [] { 5,4,3,2 };

//your current function which will return true
//when you compare lst1 and lst2, even though
//lst1 is just a subset of lst2 and is not actually equal
//as mentioned by Wim Coenen
(lst1.Count() == lst2.Count() &&
        !lst1.Except(lst2).Any()); //incorrectly returns true

//this also only checks to see if one list is a subset of another
//also mentioned by Wim Coenen
lst1.Intersect(lst2).Any(); //incorrectly returns true

//So even if order doesn't matter, you can make it matter just for
//the equality check like so:
lst1.OrderBy(x => x).SequenceEqual(lst2.OrderBy(x => x)); //correctly returns false
lst3.OrderBy(x => x).SequenceEqual(lst2.OrderBy(x => x)); // correctly returns true

---

Here's an O(n) solution that only walks each sequence once (in fact, it might not even completely walk the second sequence, it has early termination possibilities):

public static bool HaveSameItems<T>(IEnumerable<T> a, IEnumerable<T> b) {
    var dictionary = a.GroupBy(x => x).ToDictionary(g => g.Key, g => g.Count());
    foreach(var item in b) {
        int value;
        if (!dictionary.TryGetValue(item, out value)) {
            return false;
        }
        if (value == 0) {
            return false;
        }
        dictionary[item] -= 1;
    }
    return dictionary.All(x => x.Value == 0);
}

One downside to this solution is that it's not going to interop with LINQ to SQL, EF, NHiberate etc. nicely.