Question

I have an Object named Item:

public class Item
{
   public Guid Id { get; set; }
   public long Size { get; set; }       
}

in a List<Item>

What I need is to query this list and return a number of rows where the
cumulated size (Size property of Item) does not exceed a certain number (threshold).

I could then process these elements, remove them from the original list and get the next
elements with the same query until all elements have been processed.

Example List:

Id       Size
----------------
1         10
2         13
3         5
4         30
5         10

Say my desired threshold is a maximum size of 25.

The query should return the items with Id 1 & 2 since their cumulated size doesn’t exceed
25. Then I remove these two values. The next time the query should return 3 & 5.
Id 4 should never be returned since it exceeds 25.

Any ideas?

Answer 1

I think you need to store some running sum value, but TakeWhile should do the job.
Something like this:

var someValues = Enumerable.Range(0, 100);
var runningSum = 0;
var whereSumLessThan100 = someValues.TakeWhile(
    item => { runningSum += item; return runningSum < 100; }).ToList();
foreach(var item in whereSumLessThan100)
    Console.WriteLine(item);
Console.WriteLine("Sum: " + whereSumLessThan100.Sum());