UnorderedEquals method to compare 2 lists fails on Boolean values

Question

I use an UnorderedEquals extension to compare 2 lists. It works well, except where the only difference is a Boolean value. Here is the compare method:

    public static bool UnorderedEquals<T>( this IEnumerable<T> list1, IEnumerable<T> list2, IEqualityComparer<T> comparer )
    {
        var d = new Dictionary<T, int>( comparer );
        foreach( T s in list1 )
        {
            if( d.ContainsKey( s ) )
            {
                d[s]++;
            }
            else
            {
                d.Add( s, 1 );
            }
        }
        foreach( T s in list2 )
        {
            if( d.ContainsKey( s ) )
            {
                d[s]--;
            }
            else
            {
                return false;
            }
        }
        return d.Values.All( c => c == 0 );
    }

Here is my Class and IEqualityComparer:

    public class SelectedEntities
    {
        public int Id { get; set; }
        public bool IsDelegator { get; set; }
        public bool IsDelegate { get; set; }
    }

    public class SelectedEntitiesEqualityComparer : IEqualityComparer<SelectedEntities>
    {
        public bool Equals( SelectedEntities x, SelectedEntities y )
        {
            if( object.ReferenceEquals( x, y ) )
                return true;
            if( x == null || y == null )
                return false;
            return x.Id.Equals( y.Id );
        }

        public int GetHashCode( SelectedEntities obj )
        {
            return obj.Id.GetHashCode( );
        }
    }

Using this code, I should be able to get a false value from running the following:

    private bool CompareLists( )
    {
        bool result = false;

        var list1 = new List<SelectedEntities>( );
        var list2 = new List<SelectedEntities>( );

        list1.Add( new SelectedEntities { Id = 1, IsDelegator = false, IsDelegate = true } );
        list1.Add( new SelectedEntities { Id = 2, IsDelegator = false, IsDelegate = true } );

        list2.Add( new SelectedEntities { Id = 1, IsDelegator = false, IsDelegate = true } );
        list2.Add( new SelectedEntities { Id = 2, IsDelegator = false, IsDelegate = false } ); // this is different

        result = list1.UnorderedEquals( list2, new SelectedEntitiesEqualityComparer( ) );

        return result;
    }

If I change any of the Boolean values to be different between the two list, it always returns true. Bizarre.

Answer 1

Your comparer does not take into account all the fields. Currently you only compare Id. What about IsDelegator and IsDelegate?

You should add them:

public class SelectedEntitiesEqualityComparer : IEqualityComparer<SelectedEntities>
{
    public bool Equals( SelectedEntities x, SelectedEntities y )
    {
        if( object.ReferenceEquals( x, y ) )
            return true;
        if( x == null || y == null )
            return false;
        return x.Id.Equals( y.Id ) && 
               x.IsDelegator.Equals(y.IsDelegator) &&
               x.IsDelegate.Equals(y.IsDelegate);
    }

    public int GetHashCode( SelectedEntities obj )
    {
        return obj.Id.GetHashCode( )^
               obj.IsDelegator.GetHashCode()^
               obj.IsDelegate.GetHashCode();
    }
}

BTW this implementation of GetHashCode might not be optimal. For good practices regarding this look at What is the best way to implement this composite GetHashCode()

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Note Your implementation of UnorderedEquals can be shortened to this:

return list1.Count() == list2.Count() &&
       list1.All(e=> list2.Contains(e, comparer));