C# 如何将两个 IEnumerable<T> 连接成一个新的 IEnumerable<T>？
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How to concatenate two IEnumerable<T> into a new IEnumerable<T>?
提问by Samuel Rossille
I have two instances of IEnumerable<T>(with the same T). I want a new instance of IEnumerable<T>which is the concatenation of both.
我有两个IEnumerable<T>（具有相同的T）实例。我想要一个新实例，IEnumerable<T>它是两者的串联。
Is there a build-in method in .Net to do that or do I have to write it myself?
.Net 中是否有内置方法可以做到这一点，还是我必须自己编写？
采纳答案by Jon Skeet
Yes, LINQ to Objects supports this with Enumerable.Concat:
是的，LINQ to Objects 支持Enumerable.Concat：
var together = first.Concat(second);
NB: Should firstor secondbe null you would receive a ArgumentNullException. To avoid this & treat nulls as you would an empty set, use the null coalescing operator like so:
注意：应该first或second为空你会收到一个ArgumentNullException. 为了避免这种情况并像处理空集一样处理空值，请使用空值合并运算符，如下所示：
var together = (first ?? Enumerable.Empty<string>()).Concat(second ?? Enumerable.Empty<string>()); //amending `<string>` to the appropriate type
回答by Jay Shukla
You can use below code for your solution:-
您可以使用以下代码作为您的解决方案：-
public void Linq94()
{
int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };
int[] numbersB = { 1, 3, 5, 7, 8 };
var allNumbers = numbersA.Concat(numbersB);
Console.WriteLine("All numbers from both arrays:");
foreach (var n in allNumbers)
{
Console.WriteLine(n);
}
}
回答by Hasse
// The answer that I was looking for when searching
public void Answer()
{
IEnumerable<YourClass> first = this.GetFirstIEnumerableList();
// Assign to empty list so we can use later
IEnumerable<YourClass> second = new List<YourClass>();
if (IwantToUseSecondList)
{
second = this.GetSecondIEnumerableList();
}
IEnumerable<SchemapassgruppData> concatedList = first.Concat(second);
}
回答by supercat
The Concatmethod will return an object which implements IEnumerable<T>by returning an object (call it Cat) whose enumerator will attempt to use the two passed-in enumerable items (call them A and B) in sequence. If the passed-in enumerables represent sequences which will not change during the lifetime of Cat, and which can be read from without side-effects, then Cat may be used directly. Otherwise, it may be a good idea to call ToList()on Catand use the resulting List<T>(which will represent a snapshot of the contents of A and B).
该Concat方法将返回一个对象，该对象IEnumerable<T>通过返回一个对象（称为 Cat）来实现，该对象的枚举器将尝试按顺序使用两个传入的可枚举项（称为 A 和 B）。如果传入的可枚举表示的序列在 Cat 的生命周期内不会改变，并且可以无副作用地读取，那么可以直接使用 Cat。否则，它可能是一个好主意，调用ToList()上Cat，并使用所得到的List<T>（A和B的内容，这将代表一个快照）。
Some enumerables take a snapshot when enumeration begins, and will return data from that snapshot if the collection is modified during enumeration. If B is such an enumerable, then any change to B which occurs before Cat has reached the end of A will show up in Cat's enumeration, but changes which occur after that will not. Such semantics may likely be confusing; taking a snapshot of Cat can avoid such issues.
一些枚举在枚举开始时拍摄快照，如果在枚举期间修改集合，将从该快照返回数据。如果 B 是这样的可枚举，那么在 Cat 到达 A 末尾之前发生的对 B 的任何更改都将显示在 Cat 的枚举中，但之后发生的更改不会。这种语义可能会令人困惑；拍摄 Cat 快照可以避免此类问题。
