1、對集合元素合並、去重復處理
/// <summary> /// 商品 /// </summary> public class GoodsInfo { /// <summary> /// 編號 /// </summary> public string GoodsNO { get; set; } /// <summary> /// 數量 /// </summary> public decimal GoodsNum { get; set; } /// </summary> /// 描述 /// </summary> public string Desc { get; set; } /// </summary> /// 描述 /// </summary> public string Other{get;set;} } class Program { static void Main(string[] args) { List<GoodsInfo> list = new List<GoodsInfo>(); list.Add(new GoodsInfo() { GoodsNO = "NO.01", GoodsNum = 3,Desc="test1",Other="xx"}); list.Add(new GoodsInfo() { GoodsNO = "NO.02", GoodsNum = 1,Desc="test2",Other="xx"}); list.Add(new GoodsInfo() { GoodsNO = "NO.01", GoodsNum = 2,Desc="test3",Other="xx"}); list.Add(new GoodsInfo() { GoodsNO = "NO.03", GoodsNum = 4,Desc="test4",Other="xx"}); list.Add(new GoodsInfo() { GoodsNO = "NO.02", GoodsNum = 2,Desc="test5",Other="xx"}); /* var s = from p in list group p by p.GoodsNO into g select new { GoodsNO = g.Key,//對於多關鍵字 {GoodsNO,Desc}，如可從g.Key.GoodsNo,Desc=g.key.Desc
GoodsNum = g.Sum(x => x.GoodsNum), Other=g.First().Other, Desc=string.Join(",", g.Select(t => t.Desc).ToList()) }; */ var result=list.GroupBy(p => p.GoodsNO ).Select(g => new GoodsInfo { GoodsNO = g.Key, GoodsNum = g.Sum(x => x.GoodsNum),//此注意精度問題,可Math.Round(g.Sum(x => x.GoodsNum,2)
) Other = g.First().Other, Desc = string.Join(",", g.Select(t => t.Desc).ToList())}); result.ToList().ForEach(x => Console.WriteLine(x.GoodsNO + " " + x.GoodsNum + " " + x.Desc +" " +x.Other)); } }
輸出結果：
NO.01 5 test1,test3 xx
NO.02 3 test2,test5 xx
NO.03 4 test4 xx
對於 GoodsInfo 有很多字段的情況，需手動寫類似 Other=g.First().Other，不知有沒有其他方法？
參考引用：
https://blog.csdn.net/qq_24432127/article/details/82789138
https://www.cnblogs.com/yjmyzz/archive/2012/12/18/2823170.html
2、Linq 中按照多個值進行分組(GroupBy)
.GroupBy(x => new { x.Age, x.Sex })
group emp by new { emp.Age, emp.Sex } into g
// 實現多key分組的擴展函數版本
var sums = empList
.GroupBy(x => new { x.Age, x.Sex })
.Select(group => new {
Peo = group.Key, Count = group.Count()
});
foreach (var employee in sums) {
Console.WriteLine(employee.Count + ": " + employee.Peo);
}
// 實現多key分組的lambda版本
var sums2 = from emp in empList
group emp by new { emp.Age, emp.Sex } into g
select new { Peo = g.Key, Count = g.Count() };
foreach (var employee in sums) {
Console.WriteLine(employee.Count + ": " + employee.Peo);
}
轉自 http://www.cnblogs.com/beginor/archive/2009/04/24/1442939.html
https://www.cnblogs.com/IT-Bear/archive/2013/07/25/3214512.html
https://www.cnblogs.com/IT-Bear/archive/2013/07/25/3214512.html