I have a datatable with 4 columns A, B, C and D such that a particular combination of values for column A, B and C is unique in the datatable.
Objective:
Try this, I think ,this is one of the simple solutions.
int rowIndex = table.Rows.IndexOf(table.Select("A = 'foo' AND B = 'bar' AND C = 'baz'")[0]); string strD= Convert.ToString(table.Rows[rowIndex]["D"]);
Make sure,combination of values for column A, B and C is unique in the datatable.