lazily using LINQ Aggregate to reduce a List of strings to a CSV format (this is only for quick/dirty applications, it doesn't escape values)

LazyListToCsv.cs

//using System.Linq;

List<List<string>> SomeData = new List<List<string>>();

// add values (first item as column names)
SomeData.Add(new List<string>
{
    "Id",
    "Name",
    "etc"
});

string csv = SomeData.Aggregate("", (acc, list) => acc + string.Join(",", list) + "\n");