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

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 Sum(this IEnumerable collection, Func selector1, Func 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()
{
    new Stuff { X = 1, Y = 10 }, 
    new Stuff { X = 1, Y = 10 }
};

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