LINQ Select in descending order from collection, three different values that go up to the maximum va-CodePudding

For example i have a collection like this

var c1 = new Collection<int>{0,0,2,2,2,3,3,4,4,4,4,5,5,6,6,7};

I would like to get result like this

(6,5,4)

CodePudding user response：

You can do:

c1.Distinct()
    .OrderByDescending(x => x)
    .Skip(1)
    .Take(3)
    .ToList()

First remove all the duplicates, then sort despondingly. Skip(1) so that the max element is removed. Finally you can take 3 elements from the rest.

CodePudding user response：

In the old days, before LINQ, we might have done this on a sorted collection like you have:

var maxes = new int[4];
var idx = 0;
var max = 0;
foreach(var c in c1)
  if(c > max)
    max = maxes[(idx  )%4] = c;

At the end of this you'll have an array with 4 max values - the 3 you want, and the one you don't (which is in (idx - 1) % 4). I don't know if I'd use it now, but it's more efficient than a "distinct, then sort, then skip then take" approach as it does its work in a single pass