LINQ Aggregate聚合学习

太过爱你忘了你带给我的痛 2022-08-11 04:58 220阅读 0赞

using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    
    namespace ConsoleApplication1
    {
        class Program
        {
            static void Main(string[] args)
            {
                var num = Enumerable.Range(1, 5); //start,count
                foreach (var n in num)
                    Console.WriteLine(n.ToString() + ",");
                Console.WriteLine("=========================");
    
                string[] arr = { "jon", "tom", "lucy", "kitty", "jim" };
                var q = arr.Aggregate((current, next) => string.Format("{0}、{1}", current, next));
                Console.WriteLine(q);
                Console.WriteLine("=========================");
    
                var query = Enumerable.Repeat(arr, 3); //重复值的集合
                foreach (var item in query)
                    Console.WriteLine(item.Aggregate((y, x) => string.Format("{0},{1}", y, x)));
                Console.WriteLine("=========================");
    
                var result = num.Aggregate((total, next) => total * next);
                Console.WriteLine(string.Format("5的阶乘为:{0}", result)); //也就是1*2*3*4*5
                Console.WriteLine("=========================");
    
                //依次减去序列中的项
                int BaseC = 20;
                var r = num.Aggregate(BaseC, (current, next) => next <= current ? current - next : current);
                Console.WriteLine("20依次减去{1,2,3,4,5}序列的项，结果是：" + r.ToString());
                Console.WriteLine("=========================");
    
                kk();
                Console.ReadKey();
            }
    
            static void kk()
            {
                var list = new List<temp>  
                {  
                 new temp{ A=1, B=1, C="a"},  new temp{ A=1, B=2, C="a"},  
                 new temp{ A=1, B=3, C="a"},  new temp{ A=1, B=4, C="b"},  
                 new temp{ A=1, B=5, C="a"},  new temp{ A=2, B=6, C="a"},  
                 new temp{ A=2, B=7, C="b"},  new temp{ A=2, B=8, C="b"}  
                };
                var result = new List<temp>();
                var query = list.Aggregate((m, n) =>
                {
                    //m=>current(默认第一个),n=>next
                    if (m.A == n.A && m.C == n.C)
                    {
                        if (m.B == n.B - 1)
                        {
                            result.Add(m);
                            result.Add(n);
                            return n;
                        }
                        else
                        {
                            return m;
                        }
                    }
                    else
                    {
                        return n;
                    }
                });
                Console.WriteLine("A\tB\tC");
                result.Distinct().ToList().ForEach(r => Console.WriteLine("{0}\t{1}\t{2}", r.A, r.B, r.C));
            }
        }
    
        class temp
        {
            public int A { get; set; }
            public int B { get; set; }
            public string C { get; set; }
        }
    
    }

结果如下：  
![SouthEast][]

static void jj()
            {
                System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
                stopwatch.Start(); //  开始监视代码运行时间
                string[] arr = { "jon", "tom", "lucy", "kitty", "jim" };
                var query = Enumerable.Repeat(arr, 3000); //重复值的集合
                foreach (var item in query)
                    //Console.WriteLine(string.Join("、", item));
                    Console.WriteLine(item.Aggregate((current, next) => string.Format("{0}、{1}", current, next)));
                stopwatch.Stop(); //  停止监视
    
                TimeSpan timespan = stopwatch.Elapsed; //  获取当前实例测量得出的总时间
                Console.WriteLine("运行{0}秒", timespan.TotalSeconds);
            }

int[] num = { 1, 2, 3, 4, 5, 6 };
                int BaseC = 20;
                //保障不为负数
                //var r = num.Aggregate(BaseC, (current, next) => next <= current ? current - next : current);
                //Func<int, int, int> fn = (x, y) => x - y;
                //var r = num.Aggregate(BaseC, fn);
                var r = num.Aggregate(BaseC, (current, next) =>
                {
                    Console.WriteLine("current:{0},next:{1}", current, next);
                    /*
                     current:20,next:1
                     current:19,next:2
                     current:17,next:3
                     current:14,next:4
                     current:10,next:5
                     current:5,next:6
                     */
                    return current - next;
                });
    
                Console.WriteLine("20依次减去{1,2,3,4,5,6}序列的项，结果是：" + r.ToString());
                Console.WriteLine("=========================");

[SouthEast]: /images/20220810/5efcae5cd6b2454a9dc6671087d8116f.png