在列表中創建重複的項目

Question

我有以下代碼來複制列表X次的成員。

雖然它有效，但並不覺得特別乾淨。

直播的代碼示例：http://rextester.com/UIVZVX7918

public static List<ServiceEndPoint> GetServiceEndPoints() 
{ 
    const string source = "http://webSiteA.asmx,http://webSiteB.asmx"; 
    const int instances = 3; 

    var splitEndPoints = source.Split(new[] { "," }, StringSplitOptions.RemoveEmptyEntries) 
            .Select((s, i) => new ServiceEndPoint 
                   { 
                    Index = i, 
                    Uri = s 
                   }) 
                   .ToList(); 

    // Duplicate the contents of splitEndPoints "instances" number of times 
    var serviceEndPoints = new List<ServiceEndPoint>(); 
    foreach (var point in splitEndPoints) 
    { 
     for (var i = 0; i < instances; i++) 
     { 
      serviceEndPoints.Add(point); 
     } 
    } 

    return serviceEndPoints; 
} 

public class ServiceEndPoint 
{ 
    public int Index { get; set; } 
    public string Uri { get; set; } 
} 

是否有這樣做的更好的辦法？如果你喜歡通順語法

int instances = 3; 
var serviceEndPoints = 
    (from e in Enumerable.Range(0, instances) 
    from x in serviceEndPoints 
    select x) 
    .ToList(); 

或者：

var serviceEndPoints = Enumerable 
    .Range(0, instances) 
    .SelectMany(e => serviceEndPoints) 
    .ToList(); 

注意，給予相同的{ A, B, C }列表會產生像{ A, B, C, A, B, C, A, B, C }列表

Answer 1

也許沿着線的東西：

var serviceEndPoints = splitEndPoints.SelectMany(t => 
    Enumerable.Repeat(t, instances)).ToList(); 

這會給你「A，A，A，B，B，B，C，C，C」。如果你想 「A，B，C，A，B，C，A，B，C」：

var serviceEndPoints = Enumerable.Repeat(
    splitEndPoints, instances).SelectMany(t => t).ToList(); 

Answer 2

您可以用少許的Linq做到這一點。如果要產生像{ A, A, A, B, B, B, C, C, C }列表，你可以簡單地逆轉集合的順序：

var serviceEndPoints = 
    (from x in serviceEndPoints 
    from e in Enumerable.Range(0, instances) 
    select x) 
    .ToList(); 

或者用流利的語法：

var serviceEndPoints = serviceEndPoints 
    .SelectMany(x => Enumerable.Range(0, instances), (x, e) => x) 
    .ToList(); 

Answer 3

分割的兩個組件...

var parts = source.Split(new[] { "," }, StringSplitOptions.RemoveEmptyEntries); 

var serviceEndPoints = (from i in Enumerable.Range(0, instances * parts.Length) 
         let j = i/instances 
         let part = parts[j] 
         select new ServiceEndPoint { Index = j, Uri = part }).ToList(); 

或...

var parts = source.Split(new[] { "," }, StringSplitOptions.RemoveEmptyEntries); 

var serviceEndPoints2 = (from i in Enumerable.Range(0, parts.Length) 
         let part = parts[i] 
         from j in Enumerable.Range(0, instances)        
         select new ServiceEndPoint { Index = i, Uri = part }).ToList(); 

這是非常相似的兩個for一個其他:-)