Question

I have a DataTable that has a string type column filled with valid numeric values and I need to get a sum of those values. Please understand that if I was in control of the data I’m working with in this instance, I would not have used a string column to store “Cost” but that is the unfortunate reality. I’ve been using the DataTable.Compute method with the “SUM(Convert([Column],’DataType’))” expression and no filter. The problem is that I get the following exception:

System.Data.SyntaxErrorException – Syntax error in aggregate argument: Expecting a single column argument with possible ‘Child’ qualifier.

I’ve put together a small block of code that successfully reproduces the issue that I’m having.

DataTable dt = new DataTable();
            dt.Columns.Add("Cost", typeof(string));
            dt.Rows.Add(new object[] { "1" });
            dt.Rows.Add(new object[] { "3.25" });
            dt.Rows.Add(new object[] { "0.75" });

            object TotalCost = dt.Compute("Sum(Convert(Cost,'System.Decimal'))", "");

One last note, I am restricted to .NET 2.0 so using LINQ to get through this isn’t an option at the present time.

Answer 1

Wouldn’t it be simpler to define the column data type to store number, than string?

DataTable dt = new DataTable();
dt.Columns.Add("Cost", typeof(System.Decimal));
dt.Rows.Add(1M);
dt.Rows.Add(3.25M);
dt.Rows.Add(0.75M);

decimal TotalCost = (decimal)dt.Compute("Sum(Cost)", "");

EDIT: How about adding a new temporary column to do the conversion, summing it up & removing it?

DataTable dt = new DataTable();
dt.Columns.Add("Cost", typeof(string));
dt.Rows.Add(new object[] { "1" });
dt.Rows.Add(new object[] { "3.25" });
dt.Rows.Add(new object[] { "0.75" });

// temporary column for converting string to decimal
dt.Columns.Add("CostNumeric", typeof(decimal), "Convert(Cost, 'System.Decimal')");
// using temporary column to do aggregation
object TotalCost = dt.Compute("Sum(CostNumeric)", "");

dt.Columns.Remove("CostNumeric");
Console.WriteLine(TotalCost);