title: C# Deedle AggregateRowsBy Syntax
body: <p>I have a dataset like this:</p>
  
  <pre><code>Group1  Group2  Value
    A       1     350.6
    A       2     30.5
    B       1     34.1
    B       1     500.2
    C       2     20.7
    C       2     35
  </code></pre>
  
  <p>I would like to aggregate this dataset by Group1 and Group2, and then sum Value:</p>
  
  <pre><code>Group1  Group2  Value
    A       1     350.6
    A       2     30.5
    B       1     534.3
    C       2     55.7
  </code></pre>
  
  <p>I know in C# Deedle has a method called "AggregateRowsBy", however its F# syntax doesn't apply to C#. So I have tried the method like this, and it doesn't work:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Data;
  using Deedle;
  
  namespace testDeedle
  {
      class Program
      {
          static void Main(string[] args)
          {
  
            var testdata = Frame.ReadCsv(@"test_data.csv");
  
            var test2 =testdata.AggregateRowsBy(new string[2] {"Group1","Group2"},
                                              new string[1] {"Value"},
                                              x=&gt;x.NumSum());
            test2.Print();
  
          }
      }
  }
  </code></pre>
  
  <p>Unfortunately I haven't found enough online resources demonstrating the usage of Deedle in C#. Can anyone help me out? Thanks!</p>