Linq c# sum any objects from list > int

Question

I want do Linq like in topic. I have List<double> i want to check there is 2 different double which sum is more then for example 20 . i don't have idea how to do that. I create something like this

tags.Any(x => (x.Distance + tags.Select(y => y.Distance).First() > 20));

But it check only with first object, and check with myself. If 2 elements on list are the same they can be check, but with myself can't.

Can i do something like take this and next object from list?

var tags = new List<double>() {
  5, 7, 9, 13 
};

if ((i != j) && (tags(i) + tags(j)) > 20)
{

}

This link should work like this if when it would be array in a loop .

Answer 1

Try Cartesian Join ( tags with itself ):

var tags = new List<double>() {
  5, 7, 9, 13
};

var result =  tags
  .Select((a, index_a) => tags
     .Where((b, index_b) => index_a != index_b && a + b > 20)
     .Select(b => Tuple.Create(a, b)))
  .SelectMany(item => item);

// Let's have a look:
Console.Write(string.Join(Environment.NewLine, result));

Outcome:

(9, 13)
(13, 9)

if you don't want (13, 9) and alike pairs (where index_a > index_b )

var result = tags
  .Select((a, index_a) => tags
    .Skip(index_a + 1)
    .Where(b => a + b > 20)
    .Select(b => Tuple.Create(a, b)))
 .SelectMany(item => item);

// Let's have a look:
Console.Write(string.Join(Environment.NewLine, result)); 

Outcome:

(9, 13)

Answer 2

Linq is a fancy cover for for loops, foreach loops and conditional statements, as result I would construct the above question in terms of for loops and conditionals etc, then afterwards look to convert this into a Linq statement.

eg

private List<Tuple<double, double>> GetElementsWhosSumIsGreaterThanX(List<double> originalList, double x)
    {
        //take the absolute value of the variable to eliminate sign errors
        x= Math.Abs(x);

        List<Tuple<double, double>> returnList = new List<Tuple<double, double>>();

        //only go upto count - 1 as there is no more elements to compare the last element to
        for (int i = 0; i < originalList.Count - 1; i++)
        {//loop over each element in turn
            for (int j = i; j < originalList.Count - i; j++)
            {//compare it to the rest of the list from the ith element on               
                double sum = originalList[i] + originalList[j];

                if (sum> x)
                    returnList.Add( new Tuple<double, double>(originalList[i], originalList[j]));
            }
        }

        return returnList;
    }

This can be used like:

public void Test()
    {
        List<double> tags = new List<double>() {5, 7, 9, 13, 10.1, 25.6, 32.1};

        List<Tuple<double, double>> results = GetElementsWhosSumIsGreaterThanX(tags, 20);

        for (int i = 0; i < results.Count; i++)
    {
        Console.WriteLine("{0} and {1} have a sum greater than 20", results[i].Item1, results[i].Item2);
    }

    /*output:
    5 and 25.6 have a sum greater than 20
    5 and 32.1 have a sum greater than 20
    7 and 25.6 have a sum greater than 20
    9 and 13 have a sum greater than 20
    13 and 13 have a sum greater than 20
    */
    }