一个有关List<T>中元素替换的问题
现在我有两个类

    //trans
    public class Trans
    {
        public string name;
        public double fix_x;
        public double fix_y;
        public Trans(string a, double b, double c)
        {
            this.name = a;
            this.fix_x = b;
            this.fix_y = c;
        }
    }
    //Nails
    public class Nails
    {
        public string name;
        public string nail;
    }

这两个类分别用List<Trans>和List<Nails>装起来的,现在我要将List<Trans>中的name替换成List<Nails>中的nail,我写了一个实现方法,但是不知道为什么返回的还是原来的List<Trans>,求解!

        public static List<Trans> change(List<Trans> a,List<Nails> b)
        {
            List<Trans> Transf_new = new List<Trans>();
            Trans nail_new;
            
            foreach (Trans nail in a)
            {
                string c = nail.name;
                foreach (Nails net in b)
                {
                    if (nail.name == net.nail)
                        c = net.name;
                } 
 
                nail_new = new Trans(c, nail.fix_x, nail.fix_y);
                Transf_new.Add(nail_new);
            }
            return Transf_new;
        }

class list
[解决办法]
or use linq:

List<Trans> trans = new List<Trans>();
            trans.Add(new Trans("a1", 200, 300));
            trans.Add(new Trans("a2", 1200, 1300));

            List<Nails> nails = new List<Nails>();
            nails.Add(new Nails("name1", "a1"));
            nails.Add(new Nails("name2", "a2"));

            var result = from p in trans
                         from q in nails
                         where p.name == q.nail
                         select new { q.name, p.fix_x, p.fix_y };
            result.ToList().ForEach((x) =>
            {
                Console.WriteLine("name:" + x.name + " fix_x:" + x.fix_x + " fix_y:" + x.fix_y); 
 
            });

[解决办法]
本帖最后由 caozhy 于 2013-08-28 00:16:45 编辑 public static List<Trans> change(List<Trans> a,List<Nails> b)
{
return a.Join(b, x => x.name, y => y.name, (x, y) => new Trans(y.name, x.fix_x, x.fix_y)).ToList();
}

能用join就用join
join的原理是分别计算作为连接字段的hash，并且放入hash表中，所以它的算法复杂度是O(NlogN)
而你的写法包括ls的，相当于2层循环，复杂度是O(N^2)。