How to convert a column of DataTable to a List

Try this:

static void Main(string[] args)
{
    var dt = new DataTable
    {
        Columns = { { "Lastname",typeof(string) }, { "Firstname",typeof(string) } }
    };
    dt.Rows.Add("Lennon", "John");
    dt.Rows.Add("McCartney", "Paul");
    dt.Rows.Add("Harrison", "George");
    dt.Rows.Add("Starr", "Ringo");

    List<string> s = dt.AsEnumerable().Select(x => x[0].ToString()).ToList();

    foreach(string e in s)
        Console.WriteLine(e);

    Console.ReadLine();
}

var list = dataTable.Rows.OfType<DataRow>()
    .Select(dr => dr.Field<string>(columnName)).ToList();

[Edit: Add a reference to System.Data.DataSetExtensions to your project if this does not compile]

Here you go.

           DataTable defaultDataTable = defaultDataSet.Tables[0];
           var list = (from x in defaultDataTable.AsEnumerable()
                    where x.Field<string>("column1") == something
                    select x.Field<string>("column2")).ToList();

If you need the first column

           var list = (from x in defaultDataTable.AsEnumerable()
                    where x.Field<string>(1) == something
                    select x.Field<string>(1)).ToList();

Is this what you need?

DataTable myDataTable = new DataTable();
List<int> myList = new List<int>();
foreach (DataRow row in myDataTable.Rows)
{
    myList.Add((int)row[0]);
}

I do just like below, after you set your column AsEnumarable you can sort, order or how you want.

 _dataTable.AsEnumerable().Select(p => p.Field<string>("ColumnName")).ToList();