DataTable, How to conditionally delete rows

You could query the dataset and then loop the selected rows to set them as delete.

var rows = dt.Select("col1 > 5");
foreach (var row in rows)
    row.Delete();

... and you could also create some extension methods to make it easier ...

myTable.Delete("col1 > 5");

public static DataTable Delete(this DataTable table, string filter)
{
    table.Select(filter).Delete();
    return table;
}
public static void Delete(this IEnumerable<DataRow> rows)
{
    foreach (var row in rows)
        row.Delete();
}

Here's a one-liner using LINQ and avoiding any run-time evaluation of select strings:

someDataTable.Rows.Cast<DataRow>().Where(
    r => r.ItemArray[0] == someValue).ToList().ForEach(r => r.Delete());

I don't have a windows box handy to try this but I think you can use a DataView and do something like so:

DataView view = new DataView(ds.Tables["MyTable"]);
view.RowFilter = "MyValue = 42"; // MyValue here is a column name

// Delete these rows.
foreach (DataRowView row in view)
{
  row.Delete();
}

I haven't tested this, though. You might give it a try.