How can I return two fields using Linq on an object with more than two fields?

Question

What I would like to do is something I find common in MySQL which is to select all of one field distinct, and a sum of another field in that data sub-set for each unique/distinct result.

Following should replicate something simple to use in order to see the type of data I mean :

public class Stock {
   public int id {get;set;}
   public int count {get;set;}
   public string location {get;set;}
   public Stock() { }
}

public class Foo {

   public void Bar() {
        List<Stock> Stocks = new List<Stock>()
        {
            new Stock
            {
                id = 137829,
                count = 5,
                location = "Ottawa"
            },
            new Stock
            {
                id = 137829,
                count = 27,
                location = "Toronto"
            },
            new Stock
            {
                id = 137830,
                count = 8,
                location = "Toronto"
            }

        };

        var result = Stocks.DistincyBy( s => s.id);
   }
}

What I would like to store in result is as follows (using this code as an example. the real project the structure is more complex).

id = 137829, count = 32
id = 137830, count = 8

I know I can use .Sum(), but in this scenario I wish to sum where one field is distinct. How can this be achieved (i prefer my Linq to be inline syntax rather than sql style querying)

What's the difference from using `GroupBy` + `Sum`? – Ivan Stoev Jul 12 '16 at 19:34 — Ivan Stoev, Jul 12 '16 at 19:34

score 2 · Accepted Answer · answered Jul 12 '16 at 19:35

2

Use GroupBy to get the distinct groupings, then Select into your objects. For example:

var result = Stocks.GroupBy(s => s.Id).Select(g => new 
{
   Id = g.Key,
   Count = g.Sum(i => i.Count)
};

Better would be to create a named class to select into, but the syntax would be very similar.

answered Jul 12 '16 at 19:35

BradleyDotNET

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How can this be used on dynamic enumerable ? `IEnumerable result = auction.GroupBy(s => s.item).Select(g => new { Id = g.Key, Count = g.Sum(i => i.buyout) };` results in a nesting issue where `i.item` doesn't exist. The error is: The name 'item' does not exist in the current context. – Kraang Prime Jul 12 '16 at 20:14
@SanuelJackson I have no idea. An `IEnumerable` sounds like a *really* bad idea to me, let alone summing one of its properties. – BradleyDotNET Jul 12 '16 at 20:17
`JavaScriptSerializer` decoding a large JSON data set ( 6 MB ). Wouldn't mind a fast way to convert the result reliably into a typed structure. The Linq works on the first part of the enumerable, but sub-linq querying can not access the enumerator with this code. – Kraang Prime Jul 12 '16 at 20:23
@SanuelJackson How about using JsonSerializer from Newtonsoft.Json? Then its all strongly typed and LINQ works as expected. – BradleyDotNET Jul 12 '16 at 20:26
I am aware of the Json projects out there and their pluses and pitfals. I am using a class that was written by another SO user which works perfectly. I am sure there is a way to access this data and query it and / or convert the data into a strong type. I am not looking for another project just to suit that it resolves one issue :) – Kraang Prime Jul 12 '16 at 20:32
@SanuelJackson Fair enough. In case you aren't aware, Newtonsoft is used by pretty much the entire ASP.NET world. I would personally trust it over code I found on SO. Good luck with your dynamic objects though. – BradleyDotNET Jul 12 '16 at 20:37
I am aware. If curious, http://stackoverflow.com/a/3806407/3504007 is the deserialization I am using. – Kraang Prime Jul 12 '16 at 20:48

How can I return two fields using Linq on an object with more than two fields?

1 Answers1