常用Linq示例代码

   class Program

    {

        static void Main(string[] args)

        {

            //1. Aggregate

            int[] testArr = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

            //refer:http://www.cnblogs.com/ldp615/archive/2009/08/12/1544688.html

            // x is aggregate result 

            var result = Enumerable.Aggregate(testArr, (x, y) => { return x + y; });

            var result2 = Enumerable.Aggregate(testArr, calculateSum);

            string[] testStringArr = new string[] { "i", "am", "chinese" };

            var resultString = testStringArr.Aggregate((x, y) => { return x + "  " + y; });

            //2. All

            var allOK = testArr.All(o => o % 2 == 0);

            var allOK2 = testArr.All(o => o < 10);

            //3.Cast

            var testArr2 = Enumerable.Repeat(new CD() { Title = "a" }, 10);

            var ret = testArr2.Cast<ABC>().First();

            //4.group by

            var groupArr = testArr.GroupBy(o => o % 2 == 0);

            var allKeys = groupArr.Select(o => o.Key);

            var allKeysWithValues = groupArr.SelectMany(o => o.Select(x => x + " " + o.Key)).ToList();

            //5.Intersect

            int[] testArr3 = new int[] { 1, 2, 3, 9, 11, 12 };

            var intersectResult = testArr.Intersect(testArr3).ToList();

            //6.MAX, 

            var retMAX = testStringArr.Max(o => compareMAX(o));

            //7.single 

            //refer: http://blog.163.com/li_crane/blog/static/1950209720110853413858/

            //Single():操作一个集合，同时强要求只有一个对象匹配，并返回这一个。

            //First():操作一个集合，可以有多个对象匹配，但是只返回第一个。

            //Take(1):操作一个集合，可以有对个对象匹配，单只返回第一个，但是这里返回的是一个集合，而不是单个的概念。

            //8.Orderby ThenBy

            int i = 0;

            List<CD> allCDs = new List<CD>();

            while (i < 10)

            {

                allCDs.Add(new CD() { Title = i + "i", SubTitle = DateTime.Now.ToString(), TypeID = i % 3 });

                i++;

            }

            var newList = allCDs.OrderBy(o => o.SubTitle).ThenBy(o => o.Title);

            //9.ToDictionary

            var retDictionary = allCDs.ToDictionary(x => x.Title, y => y);

            //10.ToLookup

            //refer:http://blog.sina.com.cn/s/blog_5fc933730100xd3d.html

            var retLookup = allCDs.ToLookup(x => x.TypeID);

            var secondElement = retLookup[2];

            //1.Zip

            //refer:http://www.cnblogs.com/lifepoem/archive/2011/11/29/2267243.html

            IEnumerable<string> zip = testArr.Zip(allCDs, (n, w) => n + "=" + w.Title + "|" + w.SubTitle);

            foreach (var zipstr in zip)

            {

                Trace.WriteLine(zipstr);

            }

        }

        static int calculateSum(int a, int b)

        {

            return a + b;

        }

        static T compareMAX<T>(T parm)

        {

            return parm;

        }

    }

    class ABC

    {

        public string Title { get; set; }

    }

    class CD : ABC

    {

        public string SubTitle { get; set; }

        public int TypeID { get; set; }

    }

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