System.Data Namespace   DataTable Class

Computes the given expression on the current rows that pass the filter criteria.

[ VB ]
Public Function Compute ( _
   ByVal expression As String, _
   ByVal filter As String _
) As Object

[ C# ]
public object Compute (
   String expression,
   String filter
);

[ C++ ]
public: Object* Compute (
   String* expression,
   String* filter
);

[ JScript ]
public function Compute (
   expression : String,
   filter : String
) : Object;

expression

The expression to compute.

filter

The filter to limit the rows that evaluate in the expression.

An Object, set to the result of the computation.

The expression parameter requires an aggregate function. For example, the following is a legal expression:

Count ( Quantity )

But this expression is not:

Sum ( Quantity * UnitPrice )

If you must perform an operation on two or more columns, you should create a DataColumn, set its Expression property to an appropriate expression, and use an aggregate expression on the resulting column. In that case, given a DataColumn with the name "total", and the Expression property set to:

"Quantity * UnitPrice"

The expression argument for the Compute method would then be:

Sum ( total )

The second parameter filter determines which rows are used in the expression. For example, if the table contains a date column named "colDate", you could limit the rows with the following expression:

colDate > 1/1/99 AND colDate < 17/1/99

For rules on creating expressions for both parameters, see the Expression property of the DataColumn class.

The following example sums the values of a column named "Total", for the saleperson whose identification number is 5.

Private void ComputeBySalesSalesID ( DataSet myDataSet ) {
   // presumes a DataTable named "Orders" that has a column named "Total."
   DataTable myTable;
   myTable = myDataSet.Tables [ "Orders" ];
   // declare an object variable.
   object objSum;
   objSum = myTable.Compute ( "Sum ( Total ) ", "EmpID = 5" );
}

Private Sub ComputeBySalesSalesID ( ByVal myDataSet As DataSet )
   ' presumes a DataTable named "Orders" that has a column named "Total."
   Dim myTable As DataTable
   myTable = myDataSet.Tables ( "Orders" )
   ' declare an object variable.
   Dim objSum As Object
   objSum = myTable.Compute ( "Sum ( Total ) ", "EmpID = 5" )
 End Sub

DataTable Members   Expression