Question

I want to move the data from a dataColumn to a specific column in my dataTable. I am not sure how to specify what column within my Datatable I want to add the datacolumn.

        foreach (DataColumn col in dt.Columns)
        {
            dt1.Columns.Add(col);
        }

I receive an exception Column 'X' already belongs to another DataTable.

Answer 1

You need to copy the properties like ColumnName and create new DataColumns:

foreach (DataColumn col in dt.Columns)
{
    dt1.Columns.Add(col.ColumnName, col.DataType);
}

There’s a reason for the ArgumentException when you add a DataColumn which already belongs to another DataTable. It would be very dangerous to allow that since a DataTable holds a reference to their columns and every column holds a reference to it’s DataTable. If you would add a column to another table your code would blow sooner or later.

If you also want to copy the DataRows into the new table:

foreach (DataRow row in t1.Rows)
{
    var r = t2.Rows.Add();
    foreach (DataColumn col in t2.Columns)
    {
        r[col.ColumnName] = row[col.ColumnName];
    }
}