转载：http://www.cnblogs.com/ldp615/archive/2011/08/01/distinct-entension.html
只可惜linq默认不支持.Distinct(p => p.ID);
试想如果能写成下面的样子，是不是更简单优雅：
var p1 = products.Distinct(p => p.ID);
var p2 = products.Distinct(p => p.Name);
使用一个简单的 lambda 作为参数，也符合 Linq 一贯的风格。
扩展方法：
public static IEnumerable<T> Distinct<T, V>(this IEnumerable<T> source, Func<T, V> keySelector,
IEqualityComparer<V> comparer = EqualityComparer<V>.Default)
{
return source.Distinct(new CommonEqualityComparer<T, V>(keySelector, comparer));
}
using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Linq; public class CommonEqualityComparer<T, V> : IEqualityComparer<T>
{
private Func<T, V> keySelector;
private IEqualityComparer<V> comparer; public CommonEqualityComparer(Func<T, V> keySelector, IEqualityComparer<V> comparer)
{
this.keySelector = keySelector;
this.comparer = comparer;
} public CommonEqualityComparer(Func<T, V> keySelector)
: this(keySelector, EqualityComparer<V>.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));
}
}