Question

Let’s say I have a table with a Color column. Color can have various values. I have a C# method that can handle items of a given column at a time. Thus, I would like to :

foreach(colorname in mytable.getDistinctColornames)
   monocolorMethod(mytable.getSubTableOnlyContainingRowsWithColor(colorname))

How would I do that elegantly … ?

At all prices, I would avoid copying the data back & forth. I would like kind of a view on the datatable. A view that would only “show” the rows of a given columns, and a “writable” view (i.e. when I write to the filtered subset, the original table is written to)

EDIT :

Let’s say I have a ‘Car’ Table, and I would like to replace ‘Sedan’ by ‘Truck’ in column ‘Type’ for all cars with ‘Color=Red’.

How would I do given the following code ?

DataTable cars (...); // the data

DataView dv = cars.DefaultView;
dv.RowFilter = "Color='Red'";

< Here I would like to loop on the DataView>. The following code does not work :

foreach (row in dv.AsEnumerable)
{
  if(row["Type"] == "Sedan")
    row["Type"] = "Truck";
}

EDIT 2 :

Found this http://msdn.microsoft.com/fr-fr/library/system.data.dataview.allowedit.aspx which suggests

view.AllowEdit = true;
view[0].BeginEdit();
view[0]["FirstName"] = "Mary";
view[0]["LastName"] = "Jones";
view[0].EndEdit();

Answer 1

Did you try using DataView class? It looks like exactly what you want to achieve without using LINQ: http://msdn.microsoft.com/en-us/library/fdcwwhez

An example of usage:

Let say there is a DataTable object named _dt with 4 rows in it:

_dt = new DataTable("") {Columns = {new DataColumn("ID"), new DataColumn("Name"), new DataColumn("Order")}};
_dt.Rows.Add(1, "one", 1);
_dt.Rows.Add(2, "two", 3);
_dt.Rows.Add(3, "three", 2);
_dt.Rows.Add(4, "four", 5);

You can easily create DataView which doesn’t filter data but perform sorting operation on it:

_dv = new DataView(_dt, "", "Order, Name", DataViewRowState.CurrentRows);

You can also add new rows into the DataView and because it is set on corresponding DataTable that new row will be added directly to _dt object. The sorting order will be updated as well, and new row won’t be the last one within the DataView (because sort is done on Order and Name columns)

var newRow = _dv.AddNew();
newRow["ID"] = 5;
newRow["Name"] = "five";
newRow["Order"] = 4;
newRow.EndEdit();

After that code there will be 5 rows in _dt. Editing rows is also quite simple:

var editedRow = _dv[0];
editedRow.BeginEdit();
editedRow["Name"] = "Test";
editedRow.EndEdit();

You can also use DataView.Find() or DataView.FindRows() methods to find a row within the DataView.