Get sum of two columns in one LINQ query

Question

let\'s say that I have a table called Items (ID int, Done int, Total int)

I can do it by two queries:

int total = m.Items.Sum(p=>p.Total)
int done         


        

Answer 1

Figuring out where to extract the sums or other aggregate in the rest of my code confused me, until I remembered that the variable I constructed was an Iqueryable. Suppose we have a table in our database composed of Orders, and we want to produce a summary for the ABC company:

var myResult = from g in dbcontext.Ordertable
               group p by (p.CUSTNAME == "ABC") into q  // i.e., all of ABC company at once
               select new
{
    tempPrice = q.Sum( x => (x.PRICE ?? 0m) ),  // (?? makes sure we don't get back a nullable)
    tempQty = q.Sum( x => (x.QTY ?? 0m) )
};

Now the fun part -- tempPrice and tempQty aren't declared anywhere but they must be part of myResult, no? Access them as follows:

Console.Writeline(string.Format("You ordered {0} for a total price of {1:C}",
                                 myResult.Single().tempQty,
                                 myResult.Single().tempPrice ));

A number of other Queryable methods could be used as well.

Answer 2

Using the language support for tuples introduced in C# 7.0 you can solve this using the following LINQ expression:

var itemSums = m.Items.Aggregate((Total: 0, Done: 0), (sums, item) => (sums.Total + item.Total, sums.Done + item.Done));

Full code sample:

var m = new
{
    Items = new[]
    {
        new { Total = 10, Done = 1 },
        new { Total = 10, Done = 1 },
        new { Total = 10, Done = 1 },
        new { Total = 10, Done = 1 },
        new { Total = 10, Done = 1 },
    },
};

var itemSums = m.Items.Aggregate((Total: 0, Done: 0), (sums, item) => (sums.Total + item.Total, sums.Done + item.Done));

Console.WriteLine($"Sum of Total: {itemSums.Total}, Sum of Done: {itemSums.Done}");

Answer 3

When you use group by Linq creates a new collection of items so you have two collections of items.

Here's a solution to both problems:

1. summing any amount of members in one iteration and
2. avoid duplicating your item's collection

Code:

public static class LinqExtensions
{
  /// <summary>
  /// Computes the sum of the sequence of System.Double values that are obtained 
  /// by invoking one or more transform functions on each element of the input sequence.
  /// </summary>
  /// <param name="source">A sequence of values that are used to calculate a sum.</param>
  /// <param name="selectors">The transform functions to apply to each element.</param>    
  public static double[] SumMany<TSource>(this IEnumerable<TSource> source, params Func<TSource, double>[] selectors)
  {
    if (selectors.Length == 0)
    {
      return null;
    }
    else
    {
      double[] result = new double[selectors.Length];

      foreach (var item in source)
      {
        for (int i = 0; i < selectors.Length; i++)
        {
          result[i] += selectors[i](item);
        }
      }

      return result;
    }
  }

  /// <summary>
  /// Computes the sum of the sequence of System.Decimal values that are obtained 
  /// by invoking one or more transform functions on each element of the input sequence.
  /// </summary>
  /// <param name="source">A sequence of values that are used to calculate a sum.</param>
  /// <param name="selectors">The transform functions to apply to each element.</param>
  public static double?[] SumMany<TSource>(this IEnumerable<TSource> source, params Func<TSource, double?>[] selectors) 
  { 
    if (selectors.Length == 0)
    {
      return null;
    }
    else
    {
      double?[] result = new double?[selectors.Length];

      for (int i = 0; i < selectors.Length; i++)
      {
        result[i] = 0;
      }

      foreach (var item in source)
      {
        for (int i = 0; i < selectors.Length; i++)
        {
          double? value = selectors[i](item);

          if (value != null)
          {
            result[i] += value;
          }
        }
      }

      return result;
    }
  }
}

Here's the way you have to do the summation:

double[] result = m.Items.SumMany(p => p.Total, q => q.Done);

Here's a general example:

struct MyStruct
{
  public double x;
  public double y;
}

MyStruct[] ms = new MyStruct[2];

ms[0] = new MyStruct() { x = 3, y = 5 };
ms[1] = new MyStruct() { x = 4, y = 6 };

// sum both x and y members in one iteration without duplicating the array "ms" by GROUPing it
double[] result = ms.SumMany(a => a.x, b => b.y);

as you can see

result[0] = 7 
result[1] = 11

Answer 4

How about

   m.Items.Select(item => new { Total = item.Total, Done = item.Done })
          .Aggregate((t1, t2) => new { Total = t1.Total + t2.Total, Done = t1.Done + t2.Done });

Answer 5

This will do the trick:

from p in m.Items
group p by 1 into g
select new
{
    SumTotal = g.Sum(x => x.Total), 
    SumDone = g.Sum(x => x.Done) 
};

Answer 6

This has been answered already, but the other answers will still do multiple iterations over the collection (multiple calls to Sum) or create lots of intermediate objects/Tuples which may be fine, but if it isn't, then you can create an extension method (or multiple) that does it the old-fashioned way but fits well in a LINQ expression.

Such an extension method would look like this:

public static Tuple<int, int> Sum<T>(this IEnumerable<T> collection, Func<T, int> selector1, Func<T, int> selector2)
{
    int a = 0;
    int b = 0;

    foreach(var i in collection)
    {
        a += selector1(i);
        b += selector2(i);
    }

    return Tuple.Create(a, b);
}

And you can use it like this:

public class Stuff
{
    public int X;
    public int Y;
}

//...

var stuffs = new List<Stuff>()
{
    new Stuff { X = 1, Y = 10 }, 
    new Stuff { X = 1, Y = 10 }
};

var sums = stuffs.Sum(s => s.X, s => s.Y);