Using LINQ to concatenate strings

Question

What is the most efficient way to write the old-school:

StringBuilder sb = new StringBuilder();
if (strings.Count > 0)
{
    foreach (string s in strings)
    {
        sb.Append(s + ", ");
    }
    sb.Remove(sb.Length - 2, 2);
}
return sb.ToString();

...in LINQ?

Answer 1

I'm going to cheat a little and throw out a new answer to this that seems to sum up the best of everything on here instead of sticking it inside of a comment.

So you can one line this:

List<string> strings = new List<string>() { "one", "two", "three" };

string concat = strings        
    .Aggregate(new StringBuilder("\a"), 
                    (current, next) => current.Append(", ").Append(next))
    .ToString()
    .Replace("\a, ",string.Empty); 

Edit: You'll either want to check for an empty enumerable first or add an .Replace("\a",string.Empty); to the end of the expression. Guess I might have been trying to get a little too smart.

The answer from @a.friend might be slightly more performant, I'm not sure what Replace does under the hood compared to Remove. The only other caveat if some reason you wanted to concat strings that ended in \a's you would lose your separators... I find that unlikely. If that is the case you do have other fancy characters to choose from.

Answer 2

Why use Linq?

string[] s = {"foo", "bar", "baz"};
Console.WriteLine(String.Join(", ", s));

That works perfectly and accepts any IEnumerable<string> as far as I remember. No need Aggregate anything here which is a lot slower.

Answer 3

Here it is using pure LINQ as a single expression:

static string StringJoin(string sep, IEnumerable<string> strings) {
  return strings
    .Skip(1)
    .Aggregate(
       new StringBuilder().Append(strings.FirstOrDefault() ?? ""), 
       (sb, x) => sb.Append(sep).Append(x));
}

And its pretty damn fast!

Answer 4

You can combine LINQ and string.join() quite effectively. Here I am removing an item from a string. There are better ways of doing this too but here it is:

filterset = String.Join(",",
                        filterset.Split(',')
                                 .Where(f => mycomplicatedMatch(f,paramToMatch))
                       );

Answer 5

Have you looked at the Aggregate extension method?

var sa = (new[] { "yabba", "dabba", "doo" }).Aggregate((a,b) => a + "," + b);

Answer 6

return string.Join(", ", strings.ToArray());

---

In .Net 4, there's a new overload for string.Join that accepts IEnumerable<string>. The code would then look like:

return string.Join(", ", strings);