Convert `List<string>` to comma-separated string

Solution 1:

In .NET 4 you don't need the ToArray() call - string.Join is overloaded to accept IEnumerable<T> or just IEnumerable<string>.

There are potentially more efficient ways of doing it before .NET 4, but do you really need them? Is this actually a bottleneck in your code?

You could iterate over the list, work out the final size, allocate a StringBuilder of exactly the right size, then do the join yourself. That would avoid the extra array being built for little reason - but it wouldn't save much time and it would be a lot more code.

Solution 2:

The following will result in a comma separated list. Be sure to include a using statement for System.Linq

List<string> ls = new List<string>();
ls.Add("one");
ls.Add("two");
string type = ls.Aggregate((x,y) => x + "," + y);

will yield one,two

if you need a space after the comma, simply change the last line to string type = ls.Aggregate((x,y) => x + ", " + y);

Solution 3:

To expand on Jon Skeets answer the code for this in .Net 4 is:

string myCommaSeperatedString = string.Join(",",ls);