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How to make left join, group by and select with the single query?

Assume I have the following data:
var workers = new[]
{
new { Name = "John", Id = 1 },
new { Name = "Greg", Id = 2 },
new { Name = "Jack", Id = 3 },
new { Name = "Josh", Id = 4 },
new { Name = "Jill", Id = 5 },
new { Name = "Jane", Id = 6 }
};
var contracts = new[]
{
new { ContractNumber="1", WorkerId=1, ContractDate = new DateTime(2017,6,30) },
new { ContractNumber="2", WorkerId=2, ContractDate = new DateTime(2017,7,10) },
new { ContractNumber="3", WorkerId=2, ContractDate = new DateTime(2017,7,15) },
new { ContractNumber="4", WorkerId=5, ContractDate = new DateTime(2017,7,20) },
new { ContractNumber="5", WorkerId=1, ContractDate = new DateTime(2017,7,25) }
};
What I need to do is to select the first worker who has the minimum quantity of contracts where contract date greater or equals to:
var fromDate = new DateTime(2017, 7, 1);
excluding the workers with the following Id:
int[] exceptWorkerIds = new int[] {1, 4};
If several workers have a similar minimum quantity of contracts then select the worker with the first name in alphabetical order.
I resolved this task the following way.
Firstly, for each worker left join contracts. If contract exists my helper property ContractExists = 1, if not then 0.
var query =
from w in workers.Where(x => !exceptWorkerIds.Contains(x.Id))
join c in contracts.Where(x => x.ContractDate >= fromDate)
on w.Id equals c.WorkerId into workerContracts
from wc in workerContracts.DefaultIfEmpty()
select new {WorkerId = w.Id, WorkerName = w.Name, ContractExists = wc == null ? 0: 1};
This query gives me the following result:
Secondly, I group the obtained results by WorkerId, WorkerName getting the sum of contracts and order data by sum and worker name:
var result =
(from q in query
group q.ContractExists by new {q.WorkerId, q.WorkerName} into g
orderby g.Sum(), g.Key.WorkerName
select new
{
WorkerId = g.Key.WorkerId,
WorkerName = g.Key.WorkerName,
WorkerContractsCount = g.Sum()
}).ToList().Take(1);
Take(1) gives me the top 1 of resulted data:
The question: Is there a way to do it with the only query or any simpler or elegant manner then I did? If yes, does this help to boost productivity of query execution?

Rather than doing join (which multiplies the data) followed by group by you could use group join (what actually your query is using before you do from wc in workerContracts.DefaultIfEmpty()).
The other logic is pretty much the same - workerContracts.Count() gives you the desired quantity of contracts, so apply the desired order, take the first and you are done:
var result =
(from w in workers.Where(x => !exceptWorkerIds.Contains(x.Id))
join c in contracts.Where(x => x.ContractDate >= fromDate)
on w.Id equals c.WorkerId into workerContracts
let workerContractsCount = workerContracts.Count()
orderby workerContractsCount, w.Name
select new
{
WorkerId = w.Id,
WorkerName = w.Name,
WorkerContractsCount = workerContractsCount
})
.FirstOrDefault();

With maybe less Wheres and Join than Ivan Stoev's answer, here is a more compact version :
var result = workers
.Where(w => !exceptWorkerIds.Contains(w.Id))
.Select(w => new {
Name = w.Name,
Id = w.Id,
Nb = contracts
.Count(c => c.WorkerId == w.Id && c.ContractDate >= new DateTime(2017,7,1))
})
.OrderBy(w => w.Nb).ThenBy(w => w.Name).FirstOrDefault();
if(result != null)
Console.WriteLine(result.Name);
else
Console.WriteLine("Result not found");
Explanation : for each worker except the ones we don't want to check, we count the number of contract associated which date is later or equal to 2017,7,1, we then sort it by this number and by name, and take the first one.

Group BY multiple using linq [duplicate]

This question already has answers here:
Group By Multiple Columns
(14 answers)
Closed 6 years ago.
Trying to group by multiple fileds but having issues with it. I want to group by period,productcode.
var ProductUsageSummary = from b in myProductUsage
group b by b.ProductCode into g
select new
{
Period = g.Key,
Code = g.Key,
Count = g.Count(),
TotalQty = g.Sum(n => n.Qty),
Price = g.Average(n => n.Price)
};
also tried
var ProductUsageSummary = from b in myProductUsage
group b by b.Period b.ProductCode into g
select new
{
Period = g.Key(n => n.period),
Code = g.Key,
Count = g.Count(),
TotalQty = g.Sum(n => n.Qty),
Price = g.Average(n => n.Price)
};

You could create an anonymouns object to to group on multiple columns (ex... new {prop1 prop2}) , and the grouped fields can be accessed by Key.PropertyName
Try this.
var ProductUsageSummary = from b in myProductUsage
group b by new { b.Period, b.ProductCode }into g
select new
{
Period= g.Key.Period,
Code = g.Key.ProductCode ,
Count = g.Count(),
TotalQty = g.Sum(n => n.Qty),
Price = g.Average(n => n.Price)
};

This is the correct syntax using Anonymous Types :
group b by new { b.ProductCode, b.Period } into g
Then in select:
g.Key.ProductCode and g.Key.Period
Full Query:
var ProductUsageSummary = from b in myProductUsage
group b by new { b.Period b.ProductCode } into g
select new
{
Period = g.Key.Period,
Code = g.Key.ProductCode,
Count = g.Count(),
TotalQty = g.Sum(n => n.Qty),
Price = g.Average(n => n.Price)
};

how to get the number of repetitions from List<int>

List<int> ListIdProducts = new List<int>();
var IdProductKey = from a in me.ProductKeywords where a.Keyword == item.Id select a;
foreach (var item2 in IdProductKey)
{
ListIdProducts.Add(item2.Product.Value);
}
Result is:
5
6
7
5
2
5
I need to get the following 5=3, 6=1, 7=1, 2=1

Use GroupBy LINQ method:
ListIdProducts
.GroupBy(i => i)
.Select(g => new { Value = g.Key, Count = g.Count() });

var query1 = from a in ListIdProducts
group a by new { a } into g
select new
{
item = g.Key,
itemcount = g.Count()
};

This a fairly standard group-by problem.
//untested
var IdProducts = from a in me.ProductKeywords
where a.Keyword == item.Id
group by a.Product.Value into g
select g.Count();

How to write a LINQ query combining group by and aggregates?

Given the following input, how do I write a LINQ query or expression to return an aggregated result set for the quantity?
Input:
var foo = new[] { new { PO = "1", Line = 2, QTY = 0.5000 },
new { PO = "1", Line = 2, QTY = 0.2500 },
new { PO = "1", Line = 2, QTY = 0.1000 },
new { PO = "1", Line = 2, QTY = -0.1000 }
}.ToList();
Desired result:
Something along the lines of
new { PO = "1", Line = 2, QTY = 0.7500 } // .5 + .25 + .1 + -.1
How would I write it for multiple lines as well (see the object model in foo)?

How about this:
var result = foo.GroupBy(x => x.Line)
.Select(g => new { PO = g.First().PO,
Line = g.Key,
QTY = g.Sum(x => x.QTY) });
In the case you just have one Line, just add a .Single() - result is an IEnumerable of the anonymous type defined when you set up foo.
Edit:
If both PO and Line should designate different groups (PO can have different values), they both have to be part of the group key:
var result = foo.GroupBy(x => new { x.PO, x.Line})
.Select(g => new {
PO = g.Key.PO,
Line = g.Key.Line,
QTY = g.Sum(x => x.QTY)
});

var query = (from t in foo
group t by new {t.PO, t.Line}
into grp
select new
{
grp.Key.PO,
grp.Key.Line,
QTY = grp.Sum(t => t.QTY)
}).ToList()

LINQ to SQL group by with take

I have a table that looks like this:
Id GroupId Value
and it has about 100 rows
How can I return the top 10 rows for value but with no duplicating GroupId?

This should do it:
var results = table
.GroupBy(x => x.GroupId)
.Select(x => new { Row = x, Value = x.Max(y => y.Value) })
.OrderByDescending(x => x.Value)
.Select(x => x.Row)
.Take(10);
Edit: Modified to return the entire object.

Not sure if this translates to LINQ-to-SQL, but here's an idea from L2Obj
var query = (from foo in foos
group foo by foo.GroupId into fg
select fg.OrderByDescending(f => f.Value).First())
.OrderByDescending(f => f.Value)
.Take(10);
In english, it groups on the GroupId and then selects the Foo with the highest Value from each group, orders those, and then takes 10. If anything, you could get a concrete list of your objects from L2SQL and then perform the grouping in memory, should not be a performance/memory issue since you say there are only 100 rows.
For LINQ-to-SQL, you might try something like this
var sqlQuery = (from foo in foos
join y in
(from f2 in foos
join x in
(from f1 in foos
group f1 by f1.GroupId into vg
select new { GroupId = vg.Key, MaxVal = vg.Max(f => f.Value) })
on f2.GroupId equals x.GroupId
where f2.Value == x.MaxVal
group f2 by f2.GroupId into mg
select new { GroupId = mg.Key, MinId = mg.Min(f => f.Id) })
on foo.Id equals y.MinId
orderby foo.Value descending
select foo).Take(10);
This is based on a SQL query to perform the same operation
Select top 10 f.*
From Foos f
Inner Join
(Select f.GroupID, min(f.Id) as MinId
From Foos f
Inner Join
(Select GroupId, Max(Value) as MaxVal
From Foos
Group By GroupId) x
on f.GroupId = x.GroupId
and f.Value = x.MaxVal
Group By f.GroupId) y
on f.Id = y.MinId
order by f.Value desc
It basically performs two groupings. The first gets the max value for each group, the second gets the min ID for each record from each group that has the max value (in case 2 records in a group have the same value), and then selects the top 10 records.

This one will get the full row values (it's working for me with the sample data I show bellow):
static void Main(string[] args)
{
Whatever one = new Whatever() {GroupId = 1, Id = 1, Value = 2};
Whatever two = new Whatever() { GroupId = 1, Id = 2, Value = 8 };
Whatever three = new Whatever() { GroupId = 2, Id = 3, Value = 16 };
Whatever four = new Whatever() { GroupId = 2, Id = 4, Value = 7 };
Whatever five = new Whatever() { GroupId = 3, Id = 5, Value = 21 };
Whatever six = new Whatever() { GroupId = 3, Id = 6, Value = 12 };
Whatever seven = new Whatever() { GroupId = 4, Id = 7, Value = 5 };
Whatever eight = new Whatever() { GroupId = 5, Id = 8, Value = 17 };
Whatever nine = new Whatever() { GroupId = 6, Id = 9, Value = 13 };
Whatever ten = new Whatever() { GroupId = 7, Id = 10, Value = 44 };
List<Whatever> list = new List<Whatever>();
list.Add(one);
list.Add(two);
list.Add(three);
list.Add(four);
list.Add(five);
list.Add(six);
list.Add(seven);
list.Add(eight);
list.Add(nine);
list.Add(ten);
var results = (from w in list
group w by w.GroupId into g
select new { GroupId = g.Key,
Value = g.Max(w => w.Value),
Id = g.OrderBy(w=>w.Value).Last().Id }).
OrderByDescending(w=>w.Value).Take(5);
foreach (var r in results)
{
Console.WriteLine("GroupId = {0},
Id = {1},
Value = {2}",
r.GroupId, r.Id, r.Value);
}
}
Output:
GroupId = 7, Id = 10, Value = 44
GroupId = 3, Id = 5, Value = 21
GroupId = 5, Id = 8, Value = 17
GroupId = 2, Id = 3, Value = 16
GroupId = 6, Id = 9, Value = 13