关于 List<T> 中Distinct 的用法！

Question

http://www.cnblogs.com/csharpx/archive/2010/05/27/1745122.html
楼主可以看看 

Answer 1

            List<int> ss = new List<int>();
            ss.Add(1);
            ss.Add(1);
            ss.Add(2);
            ss.Add(2);
            ss.Add(3);
            ss.Add(3);
            List<int> ss1= ss.Distinct().ToList();
            //ss1里只有1，2，3

Answer 2

顾名思义，唯一啊，看微软中午msdn总知道吧

Answer 3

List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 };            IEnumerable<int> distinctAges = ages.Distinct();            Console.WriteLine("Distinct ages:");            foreach (int age in distinctAges)
            {
                Console.WriteLine(age);
            }//自定义集合要实现自定义比较器public class Product
{
    public string Name { get; set; }
    public int Code { get; set; }
}// Custom comparer for the Product class
class ProductComparer : IEqualityComparer<Product>
{
    // Products are equal if their names and product numbers are equal.
    public bool Equals(Product x, Product y)
    {        //Check whether the compared objects reference the same data.
        if (Object.ReferenceEquals(x, y)) return true;        //Check whether any of the compared objects is null.
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;        //Check whether the products' properties are equal.
        return x.Code == y.Code && x.Name == y.Name;
    }    // If Equals() returns true for a pair of objects 
    // then GetHashCode() must return the same value for these objects.    public int GetHashCode(Product product)
    {
        //Check whether the object is null
        if (Object.ReferenceEquals(product, null)) return 0;        //Get hash code for the Name field if it is not null.
        int hashProductName = product.Name == null ? 0 : product.Name.GetHashCode();        //Get hash code for the Code field.
        int hashProductCode = product.Code.GetHashCode();        //Calculate the hash code for the product.
        return hashProductName ^ hashProductCode;
    }}
Product[] products = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 }, 
                       new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "lemon", Code = 12 } };//Exclude duplicates.IEnumerable<Product> noduplicates =
    products.Distinct(new ProductComparer());foreach (var product in noduplicates)
    Console.WriteLine(product.Name + " " + product.Code);/*
    This code produces the following output:
    apple 9 
    orange 4
    lemon 12
*///以上是MSDN的示例代码，简单易读  容易上手

Answer 4

http://blog.csdn.net/q107770540/article/details/5784646

Answer 5

List<T>,时常用到,但每次都很混乱学习中,顶一下~~~

Answer 6

http://www.cnblogs.com/zhongweiv/archive/2011/11/11/IEqualityComparer.htmlhttp://www.cnblogs.com/ldp615/archive/2011/08/02/quickly-create-instance-of-iequalitycomparer-and-icomparer.html

Answer 7

多谢各位的回帖！经过各位的提示，我找到了另外一个去除重复项的方法！//实体类 
public class Province
    {
        public string id { get; set; }
        public string name { get; set; }
    }
//过滤
List<Province> newprovinceSelect = provinceSelect.GroupBy(p => p.id).Select(p => new Province { id = p.Key, name = p.FirstOrDefault().name }).ToList();

Answer 8

先写一个类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));
        }
    }在为IEnumerable<T>类型写一个扩展方法
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));
        }用法：object.Distinct(p=>p.属性).ToList();