Question

Everything worked fine until sequentce with the only element was passed to this function. The simplest way to reproduce is:

var sumOfSquares = Enumerable.Range(5, 1).Aggregate((s, i) => s + i*i);
// sumOfSquares == 5

I think this version of Aggregate should throw an Exception in case when sequence contains only one element.
Am I right or there is some details I missed ?

Answer 1

There’s another overload where you can provide an appropriate seed and obtain what I think is your desired result.

var sumOfSquares = Enumerable.Range(5, 1).Aggregate(0, (s, i) => s + i * i);

In this code, 0 is the initial seed, s is the accumulated value, i is the current item. This produces the value 25. (5, 2) produces 61, (5, 3) produces 110, etc.