发一个GroupBy动态选择多列的代码

[threenewbee]

LINQ的GroupBy需要传入一个keyselector的Lambda表达式，但是如果需要分组的条件不确定，需要通过程序输入判断，就比较麻烦了。
以前写过一个动态分组的代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;

namespace DynamicGroupBy
{
    static class LinqExt
    {
        public class DGroupBy<T> : IGrouping<object[], T>
        {
            private List<T> _innerlist = new List<T>();

            private object[] _key;

            public DGroupBy(object[] key) { _key = key; }

            public object[] Key
            {
                get { return _key; }
            }

            public void Add(T value)
            {
                _innerlist.Add(value);
            }

            public IEnumerator<T> GetEnumerator()
            {
                return this._innerlist.GetEnumerator();
            }

            System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
            {
                return this._innerlist.GetEnumerator();
            }
        }

        public static IEnumerable<IGrouping<object[], T>> DynamicGroupBy<T>(this IEnumerable<T> data, string[] keys)
        {
            List<DGroupBy<T>> list = new List<DGroupBy<T>>();

            var exps = keys.Select(x =>
            {
                var para = Expression.Parameter(typeof(T), "p");
                Expression<Func<T, object>> GetProp = Expression.Lambda<Func<T, object>>(
                    Expression.MakeMemberAccess(para, typeof(T).GetProperty(x)), para) as Expression<Func<T, object>>;
                return GetProp.Compile();
            }).ToArray();

            foreach (var item in data.Select(x => new {
                k = exps.Select(y => y(x)).ToArray(),
                v = x
            }))
            {
                DGroupBy<T> existing = list.SingleOrDefault(x => x.Key.Zip(item.k, (a, b) => a.Equals(b)).All(y => y));
                if (existing == null)
                {
                    existing = new DGroupBy<T>(item.k);
                    list.Add(existing);
                }
                existing.Add(item.v);
            }
            return list;
        }
    }

    class User
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public string City { get; set; }
        public override string ToString()
        {
            return string.Format("{0},{1},{2},{3}", ID, Name, Age ,City);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            List<User> users = new List<User>()
            {
                new User() { ID = 1, Age = 20, City = "BJ", Name = "A" },
                new User() { ID = 2, Age = 20, City = "BJ", Name = "B" },
                new User() { ID = 3, Age = 20, City = "BJ", Name = "C" },
                new User() { ID = 4, Age = 20, City = "SH", Name = "D" },
                new User() { ID = 5, Age = 30, City = "SH", Name = "E" },
                new User() { ID = 6, Age = 30, City = "SH", Name = "F" },
                new User() { ID = 7, Age = 30, City = "CD", Name = "G" },
                new User() { ID = 8, Age = 30, City = "CD", Name = "H" },
                new User() { ID = 9, Age = 30, City = "HK", Name = "I" },
                new User() { ID = 10, Age = 30, City = "HK", Name = "J" },
            };
            var query = users.DynamicGroupBy(new string[] { "City" });
            foreach (var item in query)
            {
                Console.WriteLine("Key: {0}", string.Join(",", item.Key.Select(x => x.ToString())));
                foreach (var item1 in item)
                    Console.WriteLine("\t" + item1);
            }
        }
    }
}

因为用了一些反射，效率我觉得比较低，原因是动态创建selector对象比较麻烦，后来想了想，其实不需要这么做，多次调用 GroupBy 分别按照多个字段分组，最后再Select下，把Key合并就可以了。

[peng2739956]

所以，大版主，你这贴 是想说 以前想的太多了？

[啊宝儿姐]

所以。。。。斑竹发现新大陆了

[良朋]

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[非专业开发Five]

所以这是？？？

[邓壮]

非常好的帖子哦，赞赞赞

[qzyf1992]

group by传age报错哈

[clever_yang]

，不错，不错~~

[onOneLight]