Referencing the collection your working on within LINQ - linq

Question

I am working with linq, and im wondering if there is any way that I might reference the collection I am working on from within my linq code? What I am looking for is something like this:
let result = (from t in someCollection
where t == something
select t).Where(res => res.start == THIS.Min(temp => temp.start))
So what I want to achieve in this query is that the THIS variable should provide a reference to the collection that the where clause is being applied to:
(from t in someCollection
where t == something
select t)
There are lots of ways to get around this problem, but I am specifically interested in a way of using a reference to the collection in use. Hope some of you know something about this!
Thanks!

Answer 1

The way to do what your example states is like this:
var minValue = someCollection.Min(x => x.start);
var result = from t in someCollection
where t.id > 5 // replace this line with your "where t == something"
where t.start == minValue
select t;
but say that you have to do some kind of other comparison for every
element in your collection to every other element. Is some there some
way of doing a thing like this?
If you really need to compare one item with every other item in the list, you could pattern your code like this:
var result = from t in someCollection
where t.id > 5 // replace this line with your "where t == something"
let minValue = someCollection.Min (x => x.start)
where t.start == minValue
select t;
The problem with the second example is that every item you visit in your someCollection it will be forced to recalculate the minValue.
Now, here's a completely contrived example that illustrates having to access the entire collection while accessing each member of the collection. It simply goes through a list of items and outputs each item along with all the other items that have lesser dates:
var eventItems = new[]
{
new { Name = "alpha", DateCreated = DateTime.Today.AddDays(1) },
new { Name = "bravo", DateCreated = DateTime.Today.AddDays(2) },
new { Name = "charlie", DateCreated = DateTime.Today.AddDays(-1) },
new { Name = "delta", DateCreated = DateTime.Today.AddDays(-5) },
new { Name = "echo", DateCreated = DateTime.Today.AddDays(-3) },
new { Name = "foxtrot", DateCreated = DateTime.Today.AddDays(3) },
new { Name = "golf", DateCreated = DateTime.Today.AddDays(-4) }
};
var results = from item in eventItems
where item.Name.Length > 2
let prevDays = eventItems.Where (i => i.DateCreated < item.DateCreated)
select new
{
Name = item.Name,
CurrentDate = item.DateCreated,
PreviousItems = prevDays
};
The output:
Perhaps one of these examples will help you with your exact problem.