Pivot with LINQ and anonymous type?

Question

I've searched the other "linq pivot" questions and I can't quite seem to find an exact match for mine. I need to do this with all anonymous types. I'm trying to track a checking transaction with data like the following

Check# - Step - Amount

100 - Book - 100

100 - Bank - 100

100 - Account - 100

101 - Book  - 75

101 - Bank  - 75

101 - Account  - NULL

The result I'm looking for, again, as an anonymous type is:

Check # Book   - Bank   - Account 

100 - 100 - 100- 100

101 - 75 - 75 - NULL

I really can't tell if I need to do a grouping first or not (by check#). I need it to be anonymous because I will NOT know the names of the steps as shown here. Sometimes there will 3 steps, other times there will be many more.

Answer 1

I've done something similar. Anonymous types wouldn't work since I had to do the columns dynamically and anonymous types still must be known at compile-time . The ExpandoObject , however, allows us to define properties at run-time .

I've done a quick console app as proof:

using System;
using System.Collections.Generic;
using System.Dynamic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        List<Record> input = new List<Record>();
        input.Add(new Record { CheckNumber = 100, Step = "Book", Amount = 100 });
        input.Add(new Record { CheckNumber = 100, Step = "Bank", Amount = 100 });
        input.Add(new Record { CheckNumber = 100, Step = "Account", Amount = 100 });
        input.Add(new Record { CheckNumber = 101, Step = "Book", Amount = 75 });
        input.Add(new Record { CheckNumber = 101, Step = "Bank", Amount = 75 });
        List<ExpandoObject> results = GetPivotRows(input);

        //test
        for (int i = 0; i < results.Count; i++)
        {
            dynamic record = results[i];
            Console.WriteLine("{0} - {1} - {2} - {3}", record.CheckNumber, record.Book, record.Bank, record.Account);
        }
    }

    public static List<ExpandoObject> GetPivotRows(List<Record> input)
    {
        List<string> steps = input.Select(e => e.Step).Distinct().ToList();
        Dictionary<int, ExpandoObject> outputMap = new Dictionary<int,ExpandoObject>();
        for (int i = 0; i < input.Count; i++)
        {
            dynamic row;
            if(outputMap.ContainsKey(input[i].CheckNumber))
            {
                row = outputMap[input[i].CheckNumber];
            }
            else
            {
                row = new ExpandoObject();
                row.CheckNumber = input[i].CheckNumber;
                outputMap.Add(input[i].CheckNumber, row);

                // Here we're initializing all the possible "Step" columns
                for (int j = 0; j < steps.Count; j++)
                {
                    (row as IDictionary<string, object>)[steps[j]] = new Nullable<int>();
                }
            }

            (row as IDictionary<string, object>)[input[i].Step] = input[i].Amount;
        }

        return outputMap.Values.OrderBy(e => ((dynamic)e).CheckNumber).ToList();
    }
}

public class Record
{
    public int CheckNumber { get; set; }

    public string Step { get; set; }

    public decimal Amount { get; set; }
}

Output:

100 - 100 - 100- 100

101 - 75 - 75 - 

You can use reflection to check the actual properties created in the process.

EDIT: Demystifying this a little bit - if I change that "test" loop in the main to:

for (int i = 0; i < results.Count; i++)
{
    Console.WriteLine(string.Join(" - ", results[i]));
}

I get:

[CheckNumber, 100] - [Book, 100] - [Bank, 100] - [Account, 100]
[CheckNumber, 101] - [Book, 75] - [Bank, 75] - [Account, ]

ExpandoObject implements IDictionary<string, object> behind the scenes to store whatever it needs to yet at the same time implements IDynamicMetaObjectProvider and works with dynamic binding.