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How to join two tables and group by ID and count in LINQ C# method syntax

I have two tables:
PractitionerSkill { Id, Title }
PractitionerInSkills { Id, PractitionerSkillId ), where PractitionerSkillId is FK into PractitionerSkill
(there are more columns but that is not really important)
And I'm trying to count number of skills pr practitioner.
Using LINQ method syntax, I am trying to do this:
SELECT
S.Id, S.Title, COUNT(*) as [Count] from
PractitionerSkills S INNER JOIN
PractitionerInskills PIS ON S.ID = PIS.PractitionerSkillId
GROUP BY
S.Id, S.Title
ORDER BY
S.Title
Easy in SQL. Notice that I'm getting the ID, title and count in the result.
My current efforts (which is not even method syntax)
var query = from skill in _context.PractitionerSkills
join pis in _context.PractitionerInSkills on skill.Id equals pis.PractitionerSkillId into grp
select new
{
Title = skill.Title,
Count = grp.Count()
};
which is almost there, but I can't get more columns out. I need the Skill.Id (or PractitionerInSkills.PractitionerSkillId)

It's easy in Linq too!
var query = _context.PractitionerSkills.Join(_context.PractitionerInSkills,
ps => new { k1 = ps.Id },
pis => new { k1 = pis.PractitionerSkillId },
(ps, pis) => new { ps.Id, ps.Title })
.GroupBy(r => new { r.Id, r.Title })
.Select(g => new { g.Key.Id, g.Key.Title, Count = g.Count() })
.OrderBy(r => r.Title);

C# Linq - Refactoring ForEach Loop with Sub List

Am trying to refactor some data in order to display some charts.
I can't seem to figure out why using the following, it lists all the values at the top rather than being sequential like the source data.
var categories = VehicleSales.Select(v => v.name).Distinct().ToList();
var refactoredResults = new List<StackedColumnChart>();
foreach (var category in categories)
{
var subresult = VehicleSales.Where(x => x.vehicleType == category)
.GroupBy(x => x.vehicleType)
.Select(gcs => new StackedColumnChart
{
Category = category,
Values = gcs.Select(x => (int)x.data).DefaultIfEmpty(0).ToList()
}).ToList();
refactoredResults.AddRange(subresult);
}
Source Data:
Then the actual results and expected results:
Thanks in advance!

You can do that without loop and selecting a distinct values, just use GroupBy method and map each group to StackedColumnChart using Select
var refactoredResults = VehicleSales
.GroupBy(s => s.Category)
.Select(g => new StackedColumnChart
{
Category = g.Key,
Values = g.Select(s => s.Value).ToList()
})
.ToList();
If the original data is not sorted and you'll need to sort the values by week number, you can use OrderBy clause before selecting a values Values = g.OrderBy(s => s.WeekNumber).Select(s => s.Value).ToList()

How to select multiple column and distinct one column by LINQ?

I have:
var names = db.tblPosts.Select(x => new { x.UserID, x.title }).Distinct().ToList();
I want select UserID and title and UserID is distinct.
but not worked and userID is not distinct..

var items = db.tblPosts
.GroupBy(x => x.UserId)
.Select(g => new { UserId = g.Key, Title = g.FirstOrDefault().Title })
.ToList();
It will return first Title for each UserId. Add additional OrderBy/ThenBy to sort items within group before taking first one.

How to join 3 tables with lambda expression?

I have a simple LINQ lambda join query but I want to add a 3rd join with a where clause. How do I go about doing that?
Here's my single join query:
var myList = Companies
.Join(
Sectors,
comp => comp.Sector_code,
sect => sect.Sector_code,
(comp, sect) => new {Company = comp, Sector = sect} )
.Select( c => new {
c.Company.Equity_cusip,
c.Company.Company_name,
c.Company.Primary_exchange,
c.Company.Sector_code,
c.Sector.Description
});
I want to add the following SQL command to the above LINQ query and still maintain the projections:
SELECT
sector_code, industry_code
FROM
distribution_sector_industry
WHERE
service = 'numerical'
The 3rd join would be made with Sector table & Distribution_sector_industry on sector_code.
Thanks in advance.

Just a guess:
var myList = Companies
.Join(
Sectors,
comp => comp.Sector_code,
sect => sect.Sector_code,
(comp, sect) => new { Company = comp, Sector = sect })
.Join(
DistributionSectorIndustry.Where(dsi => dsi.Service == "numerical"),
cs => cs.Sector.Sector_code,
dsi => dsi.Sector_code,
(cs, dsi) => new { cs.Company, cs.Sector, IndustryCode = dsi.Industry_code })
.Select(c => new {
c.Company.Equity_cusip,
c.Company.Company_name,
c.Company.Primary_exchange,
c.Company.Sector_code,
c.Sector.Description,
c.IndustryCode
});

Okay, I can't see why you'd want to select sector_code when you already know it, but I think you want this:
var query = from company in Companies
join sector in Sectors
on company.SectorCode equals sector.SectorCode
join industry in DistributionSectorIndustry
on sector.SectorCode equals industry.SectorCode
where industry.Service == "numerical"
select new {
company.EquityCusip,
company.CompanyName,
company.PrimaryExchange,
company.SectorCode,
sector.Description,
industry.IndustryCode
};
Notes:
I've changed it into a query expression as that's a much more readable way of expressing a query like this.
Although the "where" clause comes after the join, assuming this is a LINQ to SQL or Entity Framework query, it shouldn't make any difference
I've lengthened the range variable names for clarity
I've converted your other names into conventional .NET names; you can do this too in your model

For 4 Tables
var query = CurrencyDeposits
.Join(Customers, cd => cd.CustomerId, cus => cus.Id, (cd, cus)
=> new { CurrencyDeposit = cd, Customer = cus })
.Join(Currencies, x => x.CurrencyDeposit.CurrencyId, cr => cr.Id, (x, cr)
=> new { x.CurrencyDeposit, x.Customer, Currency = cr })
.Join(Banks, x => x.CurrencyDeposit.BankId, bn => bn.Id, (x, bn)
=> new { x.CurrencyDeposit, x.Customer, x.Currency, Bank = bn})
.Select(s => new {
s.CurrencyDeposit.Id,
s.Customer.NameSurname,
s.Currency.Code,
s.Bank.BankName,
s.CurrencyDeposit.RequesCode
});

Try something like this...
var myList = ({from a in Companies
join b in Sectors on a.Sector_code equals b.Sector_code
join c in Distribution on b.distribution_code equals a.distribution_code
select new {...});

LINQ to SQL GroupBy Max() lambda

Please help me convert this to a lambda expression
SELECT [UserID], MAX(Created) Created
FROM [UserHistory]
WHERE userid IN (14287)
GROUP BY [UserID]
Thanks!
EDIT:
Here's what I have so far.
List<T> list; //list is populated
table.Where(x => list.Select(y => y.ClientId).Contains( x.UserID))
.GroupBy(x => x.UserID)
.Select(x => new { x.UserID, x.Created })
.ToList();
When I add the GroupBy, my Select says there's no definition for x.UserID and x.Created.

Here you go:
var userIDs = new[] {14287, };
var results =
dataContext.UserHistories
.Where(user => userIDs.Contains(user.userID))
.GroupBy(user => user.userID)
.Select(
userGroup =>
new
{
UserID = userGroup.Key,
Created = userGroup.Max(user => user.Created),
});

Regarding your edit, as I said in comment, in .Select(x => new { x.UserID, x.Created }), x is no longer a UserHistory, it is IGrouping<int, UserHistory>(1), which does not have UserID and Created properties, but only Key property, which is an user id and implements IEnumerable to enumerate all items for the given key (user id).
Use #DaveShaw snippet as it is the most correct one and most efficient.
(1) I assume UserID is int.

var query = from history in context.UserHistories
where ( new[] {14287} ).Contains(history.userID)
group history by history.UserID into g
select new
{
UserId = g.Key,
MaxCreated = g.Max( x => x.Created)
};