自定义通用Distinct去除重复数据的2中方式

由于Lambda Distinct方法默认是按照集合里面的值比较的，所以当集合里面存放的是类的时候，我们一般是按照实体中的某一属性值比较，其实是用默认的Distinct也可以的，自己先定义一个实现了接口IEqualityComparer的类，然后调用Distinct的重载将这个类传递进去，但是这样太麻烦了，而且不能重用 所以参考了一些资料 整了一个程序员最爱的通用的方法

A、通过实现接口IEqualityComparer来实现此需求

代码如下：

1、先定义比较类实现IEqualityComparer

    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));
        }
    }

2、接下来扩展Distinct 实现针对实体类的属性Distinct的重载方法

public static class DistinctExtensions
    {
        public static IEnumerable<T> Distinct<T, V>(this IEnumerable<T> source, Func<T, V> keySelector)
        {
            return source.Distinct(new CommonEqualityComparer<T, V>(keySelector));
        }
        public static IEnumerable<T> Distinct<T, V>(this IEnumerable<T> source, Func<T, V> keySelector, IEqualityComparer<V> comparer)
        {
            return source.Distinct(new CommonEqualityComparer<T, V>(keySelector, comparer));
        }
    }

ok完毕，

测试数据：

List<SalesOrder> lists = new List<SalesOrder>() {
new SalesOrder(){SalesOrderNo="aaa"},
new SalesOrder(){SalesOrderNo="bbb"},
new SalesOrder(){SalesOrderNo="aaa"},
new SalesOrder()
};

var item= lists.Distinct(m => m.SalesOrderNo);

B、通过HashSet来实现 ，个人来说更喜欢第二种，虽然短小但是精悍

因为HashSet的值是不允许重复的，当你通过Add方法为HashSet添加值的时候，如果已经存在该值则会返回false，

public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            HashSet<TKey> seenKeys = new HashSet<TKey>();
            foreach (TSource element in source)
            {
                if (seenKeys.Add(keySelector(element)))
                {
                    yield return element;
                }
            }
        }

完结!thank for you