Wes' Puzzling Blog

Generic version of string.Join

Have you ever had a list of something other than strings and wanted to combine the list in someway to get a single string? You could use string.Join if you could get your list into a string[] but that is not always so easy. Usually I end up writing my own join method.

Anyway I needed to do this earlier today and I decided to use the new C# 2.0 generics feature to write a generic version of the Join function. Here is the C# code and a sample use:

  1 // Default join that takes an IEnumerable list and just takes the ToString of each item
  2 public static string Join<T>(string separator, IEnumerable<T> list)
  3 {
  4   return Join<T>(separator, list, delegate(T o) { return o.ToString(); });
  5 }
  6 // Join that takes an IEnumerable list that uses a converter to convert the type to a string
  7 public static string Join<T>(string separator, IEnumerable<T> list, Converter<T, string> converter)
  8 {
  9   StringBuilder sb = new StringBuilder();
 10   foreach (T t in list)
 11   {
 12     if (sb.Length != 0) sb.Append(separator);
 13     sb.Append(converter(t));
 14   }
 15   return sb.ToString();
 16 }
 17 static void Main(string[] args)
 18 {
 19   List<int> list = new List<int>();
 20   list.AddRange(new int[] { 10, 20, 30, 40, 50 });
 21 
 22   // Just take the ToString of each integer in the list
 23   Console.WriteLine(Join(" ", list));
 24   // Use an anonymous method to convert each integer to its hex value
 25   Console.WriteLine(Join(" ", list, delegate(int i) { return i.ToString("X"); }));
 26 }

Output:
10 20 30 40 50
A 14 1E 28 32

Hopefully this will be a handy little example for someone on how to use generics and anonymous methods in C#.