C# 扩展方法——去重（Distinct）

using System;
using System.Collections.Generic;
using System.Linq;

namespace CoSubject.Common.CommonExtensions
{
	/// 

	/// IEnumerable的Distinct扩展方法
	/// 当集合元素为对象时，可用于元素对象指定字段进行排重集
	/// 
	public static class DistinctExtensions
	{
		public static IEnumerable Distinct(this IEnumerable source, Func keySelector)
		{
			return source.Distinct(new CommonEqualityComparer(keySelector));
		}

		public static IEnumerable Distinct(this IEnumerable source,  
                Func keySelector, IEqualityComparer comparer)
		{
			return source.Distinct(new CommonEqualityComparer(keySelector, comparer));
		}
	}

	public class CommonEqualityComparer : IEqualityComparer
	{
		private Func keySelector;
		private IEqualityComparer comparer;

		public CommonEqualityComparer(Func keySelector, IEqualityComparer comparer)
		{
			this.keySelector = keySelector;
			this.comparer = comparer;
		}

		public CommonEqualityComparer(Func keySelector) : this(keySelector, EqualityComparer.Default)
		{ }

		public bool Equals(T x, T y)
		{
			return comparer.Equals(keySelector(x), keySelector(y));
		}

		public int GetHashCode(T obj)
		{
			return comparer.GetHashCode(keySelector(obj));
		}
	}
}