GroupBy with Dynamic LINQ

Dynamic LINQ using System.Linq.Dynamic

First of all, when people talk about "Dynamic LINQ" there are any number of things they could be referring to. I want to mention a tidbit about the DynamicQuery sample that is delivered with Visual Studio. In Visual Studio 2010, the sample is in the following directory:

\Program Files (x86)\Microsoft Visual Studio 10.0\Samples\

Somewhere beneath that directory you will find the CSharpSamples.zip file, which contains a LinqSamples\DynamicQuery path with the dynamic querying capability I'm referring to.  I first learned about this from Scott Guthrie's blog.

The DynamicQuery example contains the Dynamic.cs file, which is a set of extension methods and an expression language that allow you to easily manipulate LINQ queries at runtime. This is incredibly powerful but is sparsely documented and introduces a few problems I'll discuss in later posts.

Group By with Dynamic LINQ

I had a really hard time finding examples of how to group results using Dynamic LINQ, so here's a simple example I came up with:

List<Data> datalist = new List<Data>();
datalist.Add(
    new Data() { Num1 = 1, Num2 = 2, Str1 = "A", Str2 = "Red" });
datalist.Add(
    new Data() { Num1 = 2, Num2 = 5, Str1 = "A", Str2 = "Blue" });
datalist.Add(
    new Data() { Num1 = 3, Num2 = 8, Str1 = "A", Str2 = "Red" });
datalist.Add(
    new Data() { Num1 = 4, Num2 = 12, Str1 = "B", Str2 = "Red" });

var test = datalist.AsQueryable()
    .GroupBy("new(Str1,Str2)", "new(Num2,Num1)");
    .Select("new(Key.Str1, Key.Str2, Average(Num2) as SumNum, Max(Num1) as MaxNum)");

foreach (object o in test)
    Console.WriteLine(o.ToString());

In the example, the "Data" class is just a class with three properties, Num1, Num2, Str1, and Str2 to simulate a table of data. I couldn't find documentation on the GroupBy method anywhere, so I hope this helps someone else.