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Use Linq let sum to calculate an average

How to calculate sum of timedifference and average using linq let method, I tried below mentioned code it's return timedifference list only.
var query1 = from c in DBCollection.Find(Query_Collection).ToList()
let DtCreateDate = Convert.ToDateTime(c["CreatedDate"])
let DtModifiedDate = Convert.ToDateTime(c["LastModifiedDate"])
let difference = (DtModifiedDate - DtCreateDate).TotalSeconds select new { difference };

By doing the following:
var query1 = from c in DBCollection.Find(Query_Collection).ToList()
let DtCreateDate = Convert.ToDateTime(c["CreatedDate"])
let DtModifiedDate = Convert.ToDateTime(c["LastModifiedDate"])
let difference = (DtModifiedDate - DtCreateDate).TotalSeconds
let averageSum = (((DtCreateDate + DtModifiedDate) / 2) + difference) //calculate the average
select new { difference, averageSum };
Above, the 'difference' between two given dates is saved in the variable difference.
I have added another variable called 'averageSum', that now stores the value of the average between the two dates, and then adds the difference to the average.

I've don't understund how you calculate average for every row, but to accumulate custom values you can use Aggregate method as shown below:
var query1 = from c in DBCollection.Find(Query_Collection).ToList()
.Select(e => new {DtCreateDate = Convert.ToDateTime(e["CreatedDate"]), DtModifiedDate = Convert.ToDateTime(e["LastModifiedDate"])})
.Select(e => new {Diff = (e.DtModifiedDate - e.DtCreateDate).TotalSeconds, Av = 0 /* Calculate average for the row */} )
.Aggregate(new {Diff = (double) 0, Av = 0}, (group, cur) => new {Diff = group.Diff + cur.Diff, Av = group.Av + cur.Av});
Result of the statement is a single object which contais sums for difference and average on the whole list

LINQ left outer join on date not working

I have this collection of GroupedResult
IQueryable<GroupedResult> groupedResult = from p in db.Departure
group p by new { p.Terminal, p.DepartureDate, p.DepartureDate.Month } into g
select new GroupedResult
{
terminal = g.Key.Terminal.Code,
date = g.Key.DepartureDate,
distance = g.Count(),
month = g.Key.Month
};
The problem is that the collection I get has some dates missing. For example db.Departure contains Feb. 1, 2, 4, and 6. I also wanted to show GroupedResult for Feb. 3 and 5 so I use the following code to create a collection of dates starting from a particular start date:
var dates = new List<DateTime>();
for (var dt = date; dt <= DateTime.Now; dt = dt.AddDays(1))
{
dates.Add(dt);
}
And then join dates with groupedResult
var result = from p in groupedResult.ToList()
from q in dates.Where(r => r == p.date).DefaultIfEmpty()
select p;
The result I get is same as the one with groupedResult. How can I also show the entries with no date data?

This is because you are selecting P at the very end.....you have to create new anonymous class
var result = from q in dates
join p in groupedResult.ToList() on q equals p.date into joinedResult
from r in joinedResult.DefaultIfEmpty()
select new
{
terminal = r==null?null:r.terminal,
date = q,
distance = r==null?null:r.distance,
month = r==null?null:r.month
};

var result = from p in groupedResult.ToList()
from q in dates.Where(r => r == p.date).DefaultIfEmpty()
select p;
You've got the left join the wrong way around. You're selecting all items from your groupedResult and then ask LINQ to get all dates - or none if there is none - that match a date that already exists in the groupedResult.
var result = from q in dates
from p in groupedResult.Where(r => r.date == q).DefaultIfEmpty()
select new { Date = q, Items = p };
This works, because you select all dates and search for matching grouped items instead.

how to get data in monthly wise by group the month and union using joins in linq

Here unoinColumn is return the all the date with out duplicate but i want to get the date group by month
month totalamount
7/2014 10000
8/2014 10000
enter code here var unoinDateColumn = (from agent in db.collections
where agent.Date_Time.Value.Year == thisYear
select agent.Date_Time).Union(from u in db.bank_deposit
where u.Date_Time.Value.Year == thisYear
select u.Date_Time).ToList();

You can do something like that, if I understood well.
Filter collections and deposits by given year, select date_time and amount
Union, group by month, select date in the desired format, and sum amount.
You can of course do all that in one query, but I'm not sure this will be easier to read ;)
var collections = db.Collections.Where(x => x.Date_Time.Value.Year == thisYear)
.Select(m => new {
dt = m.Date_Time.Value,
amount = m.Amount
});
var deposits = db.Collections.Where(x => x.Date_Time.Value.Year == thisYear)
.Select(m => new {
dt = m.Date_Time.Value,
amount = m.Amount
});
var result = collections.Union(deposits)
.GroupBy(m => m.dt.Month)
.Select(g => new {
date = g.First().dt.ToString("MM/yyyy"),
totalAmount = g.Sum(x => x.amount)
});

How to: sum all values and assign a percentage of the total in Linq to sql

I have a simple linq query that I'm trying to extend so that I can first sum all the values in the VoteCount field and then for each Nominee I want to assign what percentage of votes the nominee received.
Here's the code:
TheVoteDataContext db = new TheVoteDataContext();
var results = from n in db.Nominees
join v in db.Votes on n.VoteID equals v.VoteID
select new
{
Name = n.Name,
VoteCount = v.VoteCount,
NomineeID = n.NomineeID,
VoteID = v.VoteID
};

Since selecting the single votes for each nominee and calculating the sum of all votes are two different tasks, I cannot think of a way of doing this efficiently in one single query. I would simply do it in two steps, as
var results = from n in db.Nominees
join v in db.Votes on n.VoteID equals v.VoteID
select new
{
Name = n.Name,
VoteCount = v.VoteCount,
NomineeID = n.NomineeID,
VoteID = v.VoteID
};
var sum = (decimal)results.Select(r=>r.VoteCount).Sum();
var resultsWithPercentage = results.Select(r=>new {
Name = r.Name,
VoteCount = r.VoteCount,
NomineeID = r.NomineeID,
VoteID = r.VoteID,
Percentage = sum != 0 ? (r.VoteCount / sum) * 100 : 0
});
You could also calculate the sum before the results (using an aggregate query), this would leave the task of summing to the Database engine. I believe that this would be slower, but you can always find out by trying :)

How to distinct select and group with castle active records?

How can I execute the following SQL-Query using LINQ or HQL?
SELECT `year`, `month`, COUNT(code_id)
FROM (SELECT DISTINCT request_codes_id AS code_id,
YEAR(requested) AS `year`, MONTH(requested) AS `month` FROM requests) r
GROUP BY `year`, `month`
ORDER BY `year`, `month`;
I tried the following:
var items = from r in TestaccountRequest.Queryable
group r by r.RequestCodeId into g
select g.First();
var grouped = from r in items
group r by r.Requested.ToString("yyyyMM") into y
select new { Year = y.First().Requested.Year, Month = y.First().Requested.Month, Count = y.Count() };
which threw a System.String ToString(System.String) NotSupportedException.
UPDATE:
The g.First() in the first LINQ-Query seems to cause the problem, because if I only run the first one I get a Code supposed to be unreachable-Exception, but if I remove the .First() it "works", but does not return what I need.

Group by an anonymous type instead:
var grouped = from r in items
group r by new { Year = r.Requested.Year,
Month = r.Requested.Month } into g
select new { g.Key.Year, g.Key.Month, Count = g.Count() };

I kinda solved it using the following:
var items = from r in TestaccountRequest.Queryable
group r by r.RequestCodeId into g
select g.ElementAt(0);
var grouped = from r in items.ToList()
group r by new { Year = r.Requested.Year,
Month = r.Requested.Month } into g
select new { g.Key.Year, g.Key.Month, Count = g.Count() };
but I gues thats not the best solution as all objects are getting fetched from the DB, but at least it is working for now, but please provide a better solution if available.
EDIT:
I now solved it using HQL:
HqlBasedQuery query = new HqlBasedQuery(typeof(ActivationCodeTestaccountRequestRecord),
"SELECT DISTINCT r.ActivationCodeId, YEAR(r.Requested), MONTH(r.Requested) " +
"FROM ActivationCodeTestaccountRequestRecord r");
var items = from object[] row in (ArrayList)ActiveRecordMediator.ExecuteQuery(query)
group row by new { Year = row[1], Month =row[2] } into g2
select new { Year = g2.Key.Year, Month = g2.Key.Month, Count = g2.Count() };