IEnumerable extension method to calculate the sum of its terms

Question

I want to create an extension method for IEnumerable that calculates the sum of its terms and returns the total value. This method must perform this sum only if type T is a numeric type (double, float, int ...) and this sum must be different if the IEnumerable is a list, a set, or a dictionary.

My attempt to create this method is just below:

public static class IEnumerableTExtensoes
{
   public static double Sum<T>(this IEnumerable<T> IEnum)
    {
        bool isInt = typeof(T) == typeof(int);
        bool isFloat = typeof(T) == typeof(float);
        bool isDouble = typeof(T) == typeof(double);

        if(isInt || isFloat || isDouble)
        {
            T sum = (double)0;
            foreach(T num in IEnum)
            {
                sum += num;
            }
        }
        return sum;
    }
}

That is not working at all.

Any suggestion?

Why don't you use LINQ Sum https://msdn.microsoft.com/en-us/library/bb549046(v=vs.110).aspx ? — Samvel Petrosov, May 22 '17 at 19:26
This already exists. Add `using System.Linq;` at the top of your C# file and just call `Sum()` on any `IEnumerable` where `T` is numeric. — 15ee8f99-57ff-4f92-890c-b56153, May 22 '17 at 19:27
That said, "not working at all" is not a very specific problem. Please try to help us help you by saying exactly what the symptoms of your problem are. — 15ee8f99-57ff-4f92-890c-b56153, May 22 '17 at 19:28
"That is not working at all" is not a problem description at all. — Mike Nakis, May 22 '17 at 19:29
Please tell us what is the purpose of this method, and why you cant use the built-in `Sum()` extension method. — Federico Dipuma, May 22 '17 at 19:30
I wouldn't like to use Sum() of "using System.Linq;". I would like to make my own method as an exercise. — Raul Figueira, May 22 '17 at 19:31
I am making that to improve my programming skills. That's why I don't want to use the Sum() from "using System.Linq;" — Raul Figueira, May 22 '17 at 19:33
I don't understand. How could you exercise if we write this method for you? — Federico Dipuma, May 22 '17 at 19:36

score 1 · Answer 1 · answered May 22 '17 at 19:36

Let me guess: this is not working because T does not define operator +.

There are two ways that I can think of that you could use to solve this, but I cannot test either one of them, so I cannot vouch as to whether each one of them will work, or whether it will turn out to be impossible due to some detail that I am missing right now.

One way would be to declare 3 separate methods:

public static double Sum(this IEnumerable<Int32> ienum),

public static double Sum(this IEnumerable<Float> ienum), and

public static double Sum(this IEnumerable<Double> ienum).

Another way would be to take advantage of the fact that all 3 types of interest implement the IConvertible interface. So, you would declare your Sum<T>() method with where T: IConvertible then within the loop you would convert each value to a known common denominator, say to Double, so that you can perform the summation, and then finally you would (somehow, I am not sure, perhaps with a cast?) convert it back to type T so you can return it.

Worth noting that `System.Linq.Enumerable` uses the many-overloads approach, not just for `Sum` but also `Min`, `Max`, and `Average` — Ben Voigt, May 22 '17 at 19:41

IEnumerable extension method to calculate the sum of its terms

1 Answers1