Question

Say I have a List of objects, and the object has a string property. I want to get a single comma-separated list of the value of each string property of each object in the list.
Here’s 1 way to do it (sans linq)

StringBuilder result = new StringBuilder()
foreach(myObject obj in myList)
{
  result.Append(obj.TheString);
  result.Append(", ");
}
// then trim the trailing ", " and call ToString() on result, etc, etc...

Here’s my first shot at linqification. Is there a better way?

string result = string.Join(", ", myList.Select(myObj => myObj.TheString).ToArray());

That’s one line of code, but it doesn’t look very efficient to me — iterate the list just to build an array, just to iterate the array and build a string… whew!

Is there a better way?

Answer 1

If you want efficient, use Enumerable.Aggregate with StringBuilder:

string result = myList.Aggregate(new StringBuilder(),
                                 (sb, o) => sb.Append(o.TheString).Append(", "))
                      .ToString();

The original problem is that String.Join wants an array. In .NET 4, there will be an overload that takes IEnumerable<string> (and I expect it will be implemented like above).