从字符串和Datatable格式化Json数据

我有一种情况，需要将json数据格式化为以下格式。

[WebMethod]
public static string ConvertDatadttoString(string appName)
{
    var sample = new List<SampleClass>
                     {
                        new SampleClass()
                            {
                                columns = new List<SampleItem>()
                                          {
                                               new SampleItem() {title = "NAME" },
                                               new SampleItem() {title = "COUNTY" },
                                          },
                                data = new List<List<string>>()
                                           {
                                               new List<string> { "John Doe", "Fresno" },
                                               new List<string> { "Billy", "Fresno" },
                                               new List<string> { "Tom", "Kern" },
                                               new List<string> { "King Smith", "Kings" },
                                           }
                            }
    };
    var serializer = new JavaScriptSerializer();
    var json = serializer.Serialize(sample);
    return json;
}
public class SampleClass
{
    public IEnumerable<SampleItem> columns { get; set; }
    public IEnumerable<IEnumerable<string>> data { get; set; }
}
public class SampleItem
{
    public string title { get; set; }
}

上面的代码为我提供了正确的json数据，但我需要对代码进行一些修改，以便它可以从我的源代码中获取数据。首先，new SampleItem() {title = "NAME" },需要从类似的字符串中填充

string columnNames = "Name,County";
string[] arrcolumnNames = columnNames.Split(',');

其次需要从.net DataTable中填充new List<string> { "John Doe", "Fresno" },。如何做到。

我尝试添加for循环并添加字符串数组中的值：

for(int i = 0; i <= arrcolumnNames.Length; i++)
{
    new SampleItem() { title = arrcolumnNames[i] }
}

但我犯了一个错误。

public static string ConvertDatadttoString(string appName = "")
{
    var columnNames = "Name,County";
    var employees = CreateEmployeesTable();
    var sample = new List<SampleClass>
    {
        new SampleClass()
        {
            columns = columnNames.Split(',').Select(x=> new SampleItem
            {
                title = x
            }),
            data = employees.AsEnumerable().Select(row=> new List<string>
            {
                row.Field<string>("EmployeeName"),
                row.Field<string>("Company")
            })
        }
    };
    var serializer = new JavaScriptSerializer();
    var json = serializer.Serialize(sample);
    return json;
}

private DataTable CreateEmployeesTable()
{
    var table = new DataTable()
    {
        Columns = { "EmployeeName", "Company" },
        TableName = "Employees"
    };
    table.Rows.Add("John Doe", "Fresno");
    table.Rows.Add("Billy", "Fresno");
    table.Rows.Add("Tom", "Kern");
    table.Rows.Add("King Smith", "Kings");
    return table;
}