C#列表<；类>；使用lambda表达式字符串的前3项

本文关键字：表达式 字符串 3项 lambda gt 列表 lt 使用 | 更新日期: 2023-09-27 17:59:51

您将如何编写方法MySpecialFunction来伴随以下代码来生成如下所示的输出？我想在逗号分隔的列表中显示前三个属性，然后计算剩余项并将其作为数字报告。我想用lambda表达式指定该属性。感谢您的帮助！

public class MyObject
{
  public Text1 {get; set;}
  public Text2 {get; set;}
  public MyObject(string text1, string text2)
  {
    Text1 = text1;
    Text2 = text2;
  }
}
public class Main()
{
  List<MyObject> myObjects = new List<MyObject>();
  myObjects.Add(new MyObject("sample11", "sample12");
  myObjects.Add(new MyObject("sample21", "sample22");
  myObjects.Add(new MyObject("sample31", "sample32");
  myObjects.Add(new MyObject("sample41", "sample42");
  myObjects.Add(new MyObject("sample51", "sample52");
  MySpecialFunction(myObjects, f => f.Text1); 
  MySpecialFunction(myObjects, f => f.Text2);
}

输出字符串为：

sample11、sample21、sample31和2个以上。

sample12、sample22、sample32和2个以上。

谢谢！

C#列表<；类>；使用lambda表达式字符串的前3项

您可以使用以下代码：

public class StackOverflow_14944788
{
    private static void MySpecialFunction(IEnumerable<MyObject> list, Func<MyObject, string> selector, int count = 3)
    {
        string result = string.Join(", ", list.Take(count).Select(selector));
        int listSize = list.Count();
        if (listSize > count)
        {
            result += ", and " + (listSize - count) + " more.";
        }
        Console.WriteLine(result);
    }
    public class MyObject
    {
        public string Text1 { get; set; }
        public string Text2 { get; set; }
        public MyObject(string text1, string text2)
        {
            Text1 = text1;
            Text2 = text2;
        }
    }
    public static void Test()
    {
        List<MyObject> myObjects = new List<MyObject>();
        myObjects.Add(new MyObject("sample11", "sample12"));
        myObjects.Add(new MyObject("sample21", "sample22"));
        myObjects.Add(new MyObject("sample31", "sample32"));
        myObjects.Add(new MyObject("sample41", "sample42"));
        myObjects.Add(new MyObject("sample51", "sample52"));
        MySpecialFunction(myObjects, f => f.Text1);
        MySpecialFunction(myObjects, f => f.Text2);
    }
}

这里有一个通用版本，它可以防止异常，并在集合中的maxCount项少于时安全地处理这种情况。它还避免了input:的多次枚举

static string MySpecialFunction<T>(IEnumerable<T> input, Func<T, string> selector, int maxCount)
{
    if (input == null)
        throw new ArgumentNullException("input");
    if (selector == null)
        throw new ArgumentNullException("selector");
    if (maxCount <= 0)
        throw new ArgumentOutOfRangeException("maxCount must be greater than 0.");
    var items = input.Select(selector).ToArray();
    if (items.Length < 1)
    {
        return string.Empty;
    }
    else if (items.Length == 1)
    {
        return items[0];
    }
    else
    {
         var joined = String.Join(", ", items, 0, Math.Min(items.Length, maxCount));
         if (items.Length > maxCount)
         {
              joined += String.Format(", and {0} more.", items.Length - maxCount);
         }
         return joined;
    }
}

你会像这样使用它：

Console.WriteLine(MySpecialFunction(myObjects, o => o.Text1, 3));

private String MySpecialFunction<T>(IEnumerable<T> items, Func<T, String> selector)
{
    var prefix = items.Take(3).Select(selector);
    var suffix = " and " + (items.Count() - 3) +" more.";
    return prefix + suffix;
}

类似的东西（请参阅运行）：

static string MySpecialFunction(IEnumerable<string> items, int limit)
{
    var sb = new StringBuilder();
    bool delimit = false;
    int count = 0;
    foreach (var item in items) {
        if (limit == 0) {
            ++count;
        } else {
            if (delimit) {
                sb.Append(", ");
            }
            delimit = true;
            sb.Append(item);
            --limit;
        }
    }
    if (count != 0) {
        sb.Append(", and ");
        sb.Append(count);
        sb.Append(" more.");
    }
    return sb.ToString();
}

然后你会这样执行：

var summary = MySpecialFunction(myObjects.Select(i => i.Text1), 3);
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