1

我想把HashSet<String>它优雅地转换成一个字符串。我可以这样迭代：

HashSet<String> words = new HashSet<string>() { "alpha", "beta", "delta" };

string joined = "";
foreach (var w in words) 
  joined += w + ",";

if(joined.Length > 0)
  joined = joined.SubString(0,joined.Length-1); // remove final comma

有没有LinQ办法优雅而有效地做到这一点？

我能想到的唯一方法是先将其转换为数组：

HashSet<String> words = new HashSet<string>() { "alpha", "beta", "delta" };
string joined = String.Join(",",words.ToArray());

但是，然后我正在做双重转换。会不会有一些方便而清晰的 LinQ 表达式？

答案 1（来自马尔的想法）

public static string JoinItems(this IEnumerable<string> items, string joiner) {
    StringBuilder sb = new StringBuilder("");

    foreach (var i in items) 
        sb.AppendFormat("{0}{1}",i,joiner);

    if(sb.Length>0) 
        return sb.Remove(sb.Length - joiner.Length, joiner.Length).ToString();
    else
       return sb.ToString();
}

ANSWER 2 使用枚举器（来自 Martin 的解决方案）

public static string JoinItems<T>(this IEnumerable<T> items, string delim) {
    var sb = new StringBuilder();
    var i = items.GetEnumerator();
    if (i.MoveNext()) {
        sb.Append(i.Current);
        while (i.MoveNext()) {
            sb.Append(delim);
            sb.Append(i.Current);
        }
    }
    return sb.ToString();
}
4

3 回答 3

3

I took your method and modified it to not need to remove the last comma. I also changed the AppendFormat to just Append because it avoids all the work of parsing the format each time.

public static string JoinItems(this IEnumerable<string> items, string joiner)
{
    StringBuilder sb = new StringBuilder(); 
    string delim = "";

    foreach (var i in items)
    {
        sb.Append(delim);
        sb.Append(i);
        delim = joiner;
    }

    return sb.ToString(); 
}
于 2010-09-16T23:25:22.527 回答
1

这将在每次迭代中无需额外的副本或检查就可以解决问题：

String JoinItems<T>(IEnumerable<T> items) {
  var stringBuilder = new StringBuilder();
  var i = items.GetEnumerator();
  if (i.MoveNext()) {
    stringBuilder.Append(i.Current);
    while (i.MoveNext()) {
      stringBuilder.Append(", ");
      stringBuilder.Append(i.Current);
    }
  }
  return stringBuilder.ToString();
}
于 2010-09-16T22:55:59.617 回答
1

我在您的 String.Join() 行中看不到双重转换。我看到一个转换ToArray()，这并不可怕，然后它执行String.Join()，它执行得很好。

.Net 4 中有一个String.Join()，它采用 IEnumerable ，无需转换即可工作。如果您使用的是较旧的框架版本，则可以为字符串编写自己的扩展方法，该方法将分隔符作为“this”参数，然后加入 IEnumerable。一定要使用 stringbuilder 来提高性能。

于 2010-09-16T19:36:37.483 回答