Is it possible to use IIF within SUM in a C# DataColumn.Expression?

Question

This is the expression I'm trying to evaluate:

Sum(IIF(QUALITY<=9.0,1.0,0.0))

The problem is that

string expr = "Sum(IIF(QUALITY<=9.0,1.0,0.0))";
dataTable.Compute(expr, "")

throws an error saying

Syntax error in aggregate argument: Expecting a single column argument with possible 'Child' qualifier.

The main challenge is that I can't rewrite the expression by hand, since it's coming to my program in a string from an RDL file, so it originally looks like

Sum(IIF(Fields!QUALITY.Value<=9.0,1.0,0.0))

and my program needs to automatically convert that into a string that will be a valid expression when passed to dataTable.Compute(). I determined from Microsoft's documentation of the Compute method that C# doesn't like the "Fields!" or ".Value" parts of the syntax, and by removing them I have simpler expressions working fine; for example, these statements both return the expected values:

dataTable.Compute("Sum(QUALITY)");
dataTable.Compute("Count(QUALITY)");

Is it possible to do what I'm trying to do? I feel like I should just need a slight change in syntax somewhere for it to work, but I haven't been able to find an answer on the internet and it's getting pretty frustrating.

Here are some of the things I've tried so far, to no avail:

Sum(IIF([QUALITY]<=9.0,1.0,0.0))
Sum(Convert(IIF(QUALITY<=9.0,1.0,0.0), 'System.Double'))
Sum(IIF(Convert(QUALITY, 'System.Double')<=9.0,1.0,0.0))    

Answer 1

One way to do this might be to add an aggregate column to the DataTable with the Expression set to IIF(QUALITY<=9.0,1.0,0.0).

dataTable.Columns.Add("AggregateColumn", typeof(double), "IIF(QUALITY<=9.0,1.0,0.0)");

then sum or count the aggregate column.

Answer 2

IIF(condition, value1, value2) returns value1 if condition is true, and value2 otherwise. Therefore, your original statement counts the number of all Quality fields with value <= 9. You can use the overload which includes a filter parameter to achieve this.

dataTable.Compute("Count(QUALITY)","QUALITY <= 9");

MSDN documentation.

Edit: Missed the dynamic requirement on the first go-round.

The error occurs because IIF makes this a two column operation, and Compute does not allow two column operations within aggregate functions. Meaning that Compute("IIF(Quality <= 9, 1, 0)") is valid, but Compute("Sum(IIF(Quality <= 9, 1, 0))") is not. You could be using IIF(Quality <= 9, Quality, SomeOtherColumn) instead of literals as the latter two arguments to IIF, and it seems that the parser doesn't know the difference.

You could use Joe's solution, or add more string processing in order to separate out coniditionals and move them to the filter parameter. Joe's answer is much more sensible than trying to reimplement the string parsing that happens behind the scenes in Compute.