string strTest = "1,2,4,6";
string Nums = strTest.Split(',');
let's create comma separated string from string Array Nums,
Generally people use foreach loop to create the comma separated string,
But here is the single line code using Lambda Expression to create the same thing.
Console.Write(Nums.Aggregate<string>((first, second) => first + "," + second));
Here the Lambda expression which is accepting two argument and returning the string having concatenation along with delimiter.