使用 Linq 枚举之前的哈希集检查计数

Question

在使用 linq 枚举哈希集之前如何查找计数？如果计数为零，我想 return 清空 code fiddle

    using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    private static HashSet<string> signalsobject = new HashSet<string>();
    public enum Signals : long
    {
        SHORT20EMASIGNAL = 2 ^ 7,
        DOUBLESHORTSIGNAL = 2 ^ 8,
    }

    ;
    public static void Main()
    {
        signalsobject.Add(Signals.SHORT20EMASIGNAL.ToString());
        signalsobject.Add(Signals.SHORT20EMASIGNAL.ToString());
        signalsobject.Remove(Signals.SHORT20EMASIGNAL.ToString());
        Console.WriteLine(signalsobject.Count);
        Console.WriteLine(signalsobject.Aggregate((a, b) => a + " " + b));
    //Console.WriteLine(signalsobject.ToString());
    //  string a = signalsobject.Count>0? (signalsobject.Aggregate((a, b) => a + " " + b)): "Empty";    
    }
}

我目前得到 [System.InvalidOperationException: 序列不包含任何元素] 在 System.Linq.Enumerable.Aggregate[TSource]（IEnumerable1 source, Func3 函数）在 Program.Main() 处：第 21 行

Answer 1

像这样？

signalsobject.Aggregate("", (a, b) => a + " " + b)

使用 Linq 枚举之前的哈希集检查计数

Hashset check count before enumerating using Linq

c#

linq