Compare Two .NET Array objects

Question

I am trying to compare two .NET arrays. Here is an obvious implementation for comparing arrays of bytes:

bool AreEqual(byte[] a, byte[] b){
    if(a.Length != b.Length)
        return false;
    foreach(int i = 0; i < a.Length; i++)
        if(a[i] != b[i])
            return false;

    return true;
}

A more refined approach can be seen here (via Google).

1. What is the simplest way (using less code but readable) to compare two .NET arrays?
2. What is the most efficient way compare two .NET arrays?

Answer 1

You could use SequenceEqual:

string[] a = { "1", "2", "3" };
string[] b = { "1", "2", "3" };

bool areEqual = a.SequenceEqual(b); // true


string[] c = { "1", "2", "5" };
areEqual = a.SequenceEqual(c);      // false

Answer 2

Kathy's approach seems a good one to me. I'd personally allow the comparer to be specified explicitly:

bool AreEqual<T>(T[] a, T[] b){
    return AreEqual(a, b, EqualityComparer<T>.Default);
}

bool AreEqual<T>(T[] a, T[] b, IEqualityComparer<T> comparer){
    if(a.Length != b.Length)
        return false;
    for(int i = 0; i < a.Length; i++)
        if(comparer.Equals(a[i], b[i])
            return false;

    return true;
}

SequenceEqual as mentioned by CMS is good, but due to its generality over IEnumerable<T> I don't think it can do the "early out" if the length aren't equal. (It's possible that it checks for both sequences implementing IList though, to check Count directly.) You could generalise a little more, to use IList<T>

bool AreEqual<T>(IList<T> a, IList<T> b, IEqualityComparer<T> comparer){
    if(a.Count != b.Count)
        return false;
    for(int i = 0; i < a.Count; i++)
        if(comparer.Equals(a[i], b[i])
            return false;

    return true;
}

The straight array version will probably be the most efficient - adding generality and abstraction usually hits performance, although whether it's significant will depend on your app.

Answer 3

Maybe something like this?

static bool AreEqual<T>(T[] a, T[] b) 
{
    bool areEqual = false ;
    T[] result = a.Intersect(b.AsEnumerable()).ToArray();
    areEqual = (result.Length == a.Length) && (result.Length == b.Length);
    return areEqual;
}

I am not sure of the performance hit on this one though.

EDIT

revised version taking into account Jon suggestions:

    static bool AreEqual<T>(T[] a, T[] b) 
    {
        return a.SequenceEqual(b);
    }

Answer 4

SequenceEqual will also make sure a and b are instanciated But it will not have the length optimisation