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POMimic `rollup` function on generic list
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  1. POMimic `rollup` function on generic list
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    copied!<p>I have a generic list of type <code>Element</code>, for example.</p> <pre><code>public class Element { public string Country { get; set; } public string City { get; set; } public int Population { get; set; } } </code></pre> <p>With the following data.</p> <pre><code>var elements = new List&lt;Element&gt; { new Element { Country = "Country A", City = "Barrie", Population = 12 }, new Element { Country = "Country A", City = "Barrie2", Population = 12 }, new Element { Country = "Country A", City = "Barrie2", Population = 12 }, new Element { Country = "Country A", City = "Barrie", Population = 12 }, new Element { Country = "Country D", City = "Essex", Population = 12 }, new Element { Country = "Country A", City = "Barrie", Population = 12 }, new Element { Country = "Country A", City = "Barrie", Population = 12 }, new Element { Country = "Country D", City = "Essex", Population = 12 }, new Element { Country = "Country A", City = "Barrie", Population = 12 }, new Element { Country = "Country A", City = "Barrie", Population = 12 } }; </code></pre> <p>Essentially, I'd like a running total of the population grouped by country and city. </p> <p>Something like.</p> <pre><code>Country A | Barrie | `running total for Barrie` Country A | Barrie2 | `running total for Barrie2` | | `total for Country A` Country D | Essex | `running total for Essex` | | `total for Country D` | | `total for everything` </code></pre> <p>I couldn't find an extension (I say extension because I plan on using a rollup several times) anywhere so I figure I'd give it a shot. So I started with this simple query.</p> <pre><code>var groupedElements = elements .GroupBy(x =&gt; new { x.Country, x.City }) .Select(x =&gt; new { Country = x.Key, City = x.Select(xx =&gt; xx.City), Population = x.Sum(xx =&gt; xx.Population) }) .ToList(); </code></pre> <p>This query works as expected so I think I'm on the right track. Next I think I have to figure out which property from <code>groupedElements</code> is aggregate because that's what we'll be doing a rollup on. How do I accomplish that? Or perhaps I could have a parameter that makes me specify what column I wish to do the aggregate function on.</p>
 

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