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How do I to use Where, Group By, Select and OrderBy at same query linq?

I'm trying to make a linq using where, group by and select at same time but I cannot do it works and it always throws an exception.
How could I do it works ?
Linq
public ActionResult getParceiros(){
//return all partners
IList<ViewParceirosModel> lista = new List<ViewParceirosModel>();
lista = context.usuarios.Where(u => u.perfil == RoleType.Parceiro)
.Select(x => new ViewParceirosModel
{
id = x.id,
nomeParceiro = x.nome,
emailAcesso = x.email
})
.GroupBy(x => x.id)
.OrderBy(x => x.nomeParceiro)
.ToList();
return View(lista);
}
Exception

Your program doesn't do what you want. Alas you forgot to tell you what you want, you only showed us what you didn't want. We'll have to guess.
So you have a sequence of Usarios.
IQueryable<Usario> usarios = ...
I don't need to know what a Usario is, all I need to know is that it has certain properties.
Your first step is throwing away some Usarios using Where: you only want to keep thos usarios that have a Perfil equal to RoleType.Parceirdo:
// keep only the Usarios with the Perfil equal to RoleType.Parceirdo:
var result = usarios.Where(usario => usario.Perfil == RoleType.Parceirdo)
in words: from the sequence of Usarios keep only those Usarios that have a Perfil equal to RoleTyoe.Parceirdo.
The result is a subset of Usarios, it is a sequence of Usarios.
From every Usario in this result, you want to Select some properties and put them into one ViewParceirosModel:
var result = usarios.Where(usario => usario.Perfil == RoleType.Parceirdo)
.Select(usario => new ViewParceirosModel
{
Id = x.id,
NomeParceiro = x.nome,
EmailAcesso = x.email,
})
In words: from every Usario that was kept after your Where, take the Id, the Nome and the Email to make one new ViewParceirosModel.
The result is a sequence of ViewParceirosModels. If you add ToList(), you can assign the result to your variable lists.
However your GroupBy spoils the fun
I don't know what you planned to do, but your GroupBy, changes your sequence of ViewParceirosModels into a sequence of "groups of ViewParceirosModels" Every ViewParceirosModel in one group has the same Id, the value of this Id is in the Key.
So if after the GroupBy you have a group of ViewParceirosModel with a Key == 1, then you know that every ViewParceirosModel in this group will have an Id equal to 1.
Similarly all ViewParceirosModel in the group with Key 17, will have an Id equal to 17.
I think Id is your primary key, so there will only be one element in each group. Group 1 will have the one and only ViewParceirosModel with Id == 1, and Group 17 will have the one and only ViewParceirosModel with Id == 17.
If Id is unique, then GroupBy is useless.
After the GroupBy you want to Order your sequence of ViewParceirosModels in ascending NomeParceiro.
Requirement
I have a sequence of Usarios. I only want to keep those Usarios with a Perfil value equal to RoleType.Parceirdo. From the remaining Usarios, I want to use the values of properties Id / Nome / Email to make ViewParceirosModels. The remaining sequence of ViewParceirosModels should be ordered by NomeParceiro, and the result should be put in a List.
List<ViewParceirosModel> viewParceiroModels = Usarios
.Where(usario => usario.Perfil == RoleType.Parceirdo)
.Select(usario => new ViewParceirosModel
{
Id = x.id,
NomeParceiro = x.nome,
EmailAcesso = x.email,
}
.OrderBy(viewParceirosModel => viewParceirosModel.NomeParceiro)
.ToList();

When you create a LINQ query with group by clause, you receive as result a grouped query.
It is a kind of dictionary that has as key the field you chose to group and as value a list of records of this group.
So, you cannot order by "nomeParceiro" because this field is inside the group.
If you detail how you expect the result I can show you a code example for this.
You can find more details in this section of the doc: https://learn.microsoft.com/pt-br/dotnet/csharp/linq/group-query-results

Let's say ViewParceirosModel look like
public class ViewParceirosModel
{
public int id {get; set;}
public List<string> nomeParceiro {get; set;}
public List<string> emailAcesso {get; set;}
}
After that, you can Groupby then select combine with Orderby like below
IList<ViewParceirosModel> lista = new List<ViewParceirosModel>();
lista = context.usuarios.Where(u => u.perfil == RoleType.Parceiro)
.Select(x => new ViewParceirosModel
{
id = x.id,
nomeParceiro = x.nome,
emailAcesso = x.email
})
.GroupBy(x => x.id)
.Select(g => new ViewParceirosModel
{
id = g.Key,
nomeParceiro = g.Select(p => p.nomeParceiro).OrderBy(x => x.nomeParceiro).ToList()
nomeParceiro = g.Select(p => p.emailAcesso).ToList()
})
.ToList();

You can use the following code.
IList<ViewParceirosModel> lista = new List<ViewParceirosModel>();
lista = context.usuarios.Where(u => u.perfil == RoleType.Parceiro)
.Select(x => new ViewParceirosModel
{
id = x.id,
nomeParceiro = x.nome,
emailAcesso = x.email
})
.OrderBy(x => x.nomeParceiro)
.GroupBy(x => x.id)
.ToList();
or
List<List<ViewParceirosModel>> listb = context.usuarios
.Where(u => u.perfil == RoleType.Parceiro)
.GroupBy(g => g.id).OrderBy(g => g.Key)
.Select(g => g.OrderBy(x => x.nomeParceiro)).ToList();

Linq to Entities group query giving list of results in each group

If I have a set of entities with 3 properties (Id, Type, Size) all of which are strings.
Is there a way using Linq to Entities where I can do a group query which gives me the Size + Type as the key and then a list of the related Id's for that Size + Type?
Example below of getting the count:
Items.GroupBy(x => new { x.Size, x.Type})
.Select(x => new { Key = x.Key, Count = x.Count() })
but I am looking to get a list of the Ids for each grouping?
I am looking to see if it is possible using Linq-to-EF before I decide to iterate through this in code and build up the result instead.

If you want to get List of Ids for each group then you have to select x.Select(r => r.Id) like:
var result = Items.GroupBy(x => new { x.Size, x.Type })
.Select(x => new
{
Key = x.Key,
Ids = x.Select(r => r.Id)
});

Another way to build up a Dictionary<string, IEnumerable<string?>> in dotnet 6.0 according to the docs;
where we have the dictionary Key as {Size, Type} and Value the list of Ids, you can write:
Dictionary<string, IEnumerable<string?>> result = Items.GroupBy(item => new { item.Size, item.Type }
item => item.Id),
(itemKey, itemIds) =>
{
Key = itemKey,
Ids = itemIds
})
.ToDictionary(x => x.Key, x=> x.Ids);

LINQ query has me baffled

How would I write a LINQ query to do the following?
I have a database table with a schema like this:
ID - Int
Time - DateTime
RecordType - Int
Msg - String
I want to get the newest (using 'Time' field) record for each 'RecordType'
Another restriction is that I'm only interested in certain RecordTypes - those contained in an int array.
The result of the query would be one record per RecordType - the newest record for this type.

var results = source.GroupBy(x => x.RecordType)
.Where(g => myRecordTypes.Contains(g.Key))
.Select(g => g.OrderByDescending(x => x.Time).First())
.ToList();
myRecordTypes is int[] with a set of RecordTypes you'd like to get as a result.
result will be List<Record> with one item per RecordType.
You can change to it to be e.g. Dictionary<int, Recort> by RecordType:
var results = source.GroupBy(x => x.RecordType)
.Where(g => myRecordTypes.Contains(g.Key))
.Select(g => new { g.Key, item = g.OrderByDescending(x => x.Time).First() })
.ToDictionary(x => x.Key, x => x.item);

Group them by record types, filter out the ones you want, and then select out the first of the items in that group ordered by time.
int[] recordTypes = GetRecordTypes();
var query = context.Table.GroupBy(item => item.RecordType)
.Where(group => recordTypes.Contains(group.Key))
.Select(group => group.OrderBy(item => item.Time).FirstOrDefault());

LINQ: how to get a group of a table ordering with a related table?

I have a doubt about the object IGrouping that results from a linq where I use a "group by" sentence.
I have two tables in the database, Products and Responses they have a relationship 1 to *. In the Responses table we have a column called FinalRate which is the rate of the product. The products can have n responses or rates.
I want to get the Products order by the sum of the FinalRate divided by the number of rates done. That is to say, order by the average rate descending from higher to lower marks.
As it can be read in the code (at the end of the question), I try to get the responses first. To sum all the finalrates and divide them by the count I use a group.
There are 2 problems with the code, even if the current code works:
1.-I tried to get the Products in a single query but it is impossible because I can not use the products table in the group and then use the Response table in the "orderby". One more thing LINQ only gives you the possibility to group one table, it is imposible to have "group prod, response".
I couldn't get this sql sentence in LINQ:
select prod.ProductID,prod.Commercial_Product_Name,prod.Manufacturer_Name,
prod.ProductImageUrl
from rev_product prod
inner join rev_response res on res.AtProductid=prod.ProductID
group by prod.ProductID,prod.Commercial_Product_Name,prod.Manufacturer_Name
,prod.ProductImageUrl
order by (sum(res.FinalRate)/count(res.AtProductid))
I tried this:
var gruposproductos = (from prod in ctx.Products
join res in ctx.Responses on prod.ProductID equals res.AtProductId
group prod by prod.ProductID into g
orderby (g.Sum(ra =>ra.FinalRate)/g.Count())
descending select g).Take(2);
But as I say, the "orderby (g.Sum..." gives an error, because "into g" groups the Product table, not the Response Table.
So this is why in my final code I don't get the products in the same LINQ sentence.
2.-Once accepted this fact, the problem is that I get an IGrouping, but I don't obtain a list of Responses that I can iterate without doing the two foreach in the code. I wanted only one loop, as one would do if you had a "List" object.
It is not really a cool method but it works. Moreover, I have to control that in the second loop there is only added 1 time.
Any better code?
var groupproducts = (from res in ctx.Responses
group res by res.AtProductId into g
orderby (g.Sum(ra =>ra.FinalRate)/g.Count())
descending select g).Take(2).ToList();
List<Product> theproducts = new List<Product>();
foreach (var groupresponse in groupproducts)
{
foreach (var response in groupresponse)
{
var producttemp= (from prod in ctx.Products
where prod.ProductID == response.AtProductId
select prod).First();
theproducts.Add(producttemp);
}
}
}
FINAL SOLUTION (thx a lot #Daniel)
var productsanonymtype = ctx.Products.Select(x => new
{
Product = x,
AverageRating = x.Responses.Count() == 0 ? 0 : x.Responses.Select(r => (double)r.FinalRate).Sum() / x.Responses.Count()
}).OrderByDescending(x => x.AverageRating);
List<Product> products = new List<Product>();
foreach (var prod in productsanonymtype)
{
products.Add(prod.Product);
}

Try this:
products.Select(x => new
{
Product = x,
AverageRating = x.Responses.Sum(x => x.FinalRate) /
x.Responses.Count()
});
The Sum overload I am using is not implemented in all providers. If that's a problem for you, you can use this alternate version:
products.Select(x => new
{
Product = x,
AverageRating = x.Responses.Select(x => x.FinalRate)
.Sum() /
x.Responses.Count()
});
If there is no navigation property from product to its responses you should first try to fix that. If you can't you can use this version:
products.Join(responses, x => x.Id, x => x.ProductId,
(p, r) => new { Product = p, Response = r })
.GroupBy(x => x.Product)
.Select(g => new { Product = g.Key,
AverageRating = g.Select(x => x.Response.FinalRate)
.Sum() /
g.Count()
});
Assuming FinalRate is an int, both methods will calculate the average rating with an int, i.e. there will be no 4.5 rating. And there will be no rounding, i.e. an actual average rating of 4.9 will result in 4. You can fix that by casting one of the operands of the division to double.
Another problem is the case with no ratings so far. The code above will result in an exception in this case. If that's a problem for you, you can change the calculation to this:
AverageRating = g.Count() == 0
? 0
: g.Select(x => (double)x.Response.FinalRate).Sum() / g.Count()

ctx.Products.GroupBy(x => new {
ProductId = x.ProductId,
FinalRate = x.Responses.Sum(y => y.FinalRate),
CountProductId = x.Responses.Count
})
.OrderBy(x => x.Key.FinalRate / x.Key.CountProductId);
And here with the projection.....
ctx.Products.Select(x => new {
ProductID = x.ProductID,
Commercial_Product_Name = x.Commercial_Product_Name,
Manufacturer_Name = x.Manufacturer_Name,
ProductImageUrl = x.ProductImageUrl,
FinalRate = x.Responses.Sum(y => y.FinalRate),
CountProductId = x.Responses.Count
})
.GroupBy(x => new {
ProductId = x.ProductId,
FinalRate = x.FinalRate,
CountProductId = x.CountProductId
})
.OrderBy(x => x.Key.FinalRate / x.Key.CountProductId);

How do I .OrderBy() and .Take(x) this LINQ query?

The LINQ query below is working fine but I need to tweak it a bit.
I want all the records in the file grouped by recordId (a customer number) and then ordered by, in descending order, the date. I'm getting the grouping and the dates are in descending order. Now, here comes the tweaking.
I want the groups to be sorted, in ascending order, by recordId. Currently, the groups are sorted by the date, or so it seems. I tried adding a .OrderBy after the .GroupBy and couldn't get that to work at all.
Last, I want to .take(x) records where x is dependent on some other factors. Basically, the .take(x) will return the most-recent x records. I tried placing a .take(x) in various places and I wasn't getting the correct results.
var recipients = File.ReadAllLines(path)
.Select (record => record.Split('|'))
.Select (tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
recordId = tokens[13],
date = Convert.ToDateTime(tokens[17])
}
)
.OrderByDescending (m => m.date)
.GroupBy (m => m.recordId)
.Dump();
Edit #1 -
recordId is not unique. There may / will likely be multiple records with the same recordId. recordId is actually a customer number.
The output will be a resultset with first name, last name, date, and recordId. Depending on several factors, there many be 1 to 5 records returned for each recordId.
Edit #2 -
The .Take(x) is for the recordId. Each recordId may have multiple rows. For now, let's assume I want the most recent date for each recordId. (select top(1) when sorted by date descending)
Edit #3 -
The following query generates the following results. Note each recordId only produces 1 row in the output (this is okay) and it appears it is the most recent date. I haven't thouroughly checked this yet.
Now, how do I sort, in ascending order, by recordId?
var recipients = File.ReadAllLines(path)
.Select (record => record.Split('|'))
.Select (tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
recordId = Convert.ToInt32(tokens[13]),
date = Convert.ToDateTime(tokens[17])
}
)
.GroupBy (m => m.recordId)
.OrderByDescending (m => m.Max (x => x.date ) )
.Select (m => m.First () )
.Dump();
FirstName LastName recordId date
X X 2531334 3/11/2011 12:00:00 AM
X X 1443809 10/18/2001 12:00:00 AM
X X 2570897 3/10/2011 12:00:00 AM
X X 1960526 3/10/2011 12:00:00 AM
X X 2475293 3/10/2011 12:00:00 AM
X X 2601783 3/10/2011 12:00:00 AM
X X 2581844 3/6/2011 12:00:00 AM
X X 1773430 3/3/2011 12:00:00 AM
X X 1723271 2/4/2003 12:00:00 AM
X X 1341886 2/28/2011 12:00:00 AM
X X 1427818 11/15/1986 12:00:00 AM

You can't that easily order by a field which is not part of the group by fields. You get a list for each group. This means, you get a list of date for each recordId.
You could order by Max(date) or Min(date).
Or you could group by recordId and date, and order by date.
order by most recent date:
.GroupBy (m => m.recordId)
// take the most recent date in the group
.OrderByDescending (m => m.Max(x => x.date))
.SelectMany(x => x.First
The Take part is another question. You could just add Take(x) to the expression, then you get this number of groups.
Edit:
For a kind of select top(1):
.GroupBy (m => m.recordId)
// take the most recent date in the group
.OrderByDescending (m => m.Max(x => x.date))
// take the first of each group, which is the most recent
.Select(x => x.First())
// you got the most recent record of each recordId
// and you can take a certain number of it.
.Take(x);
snipped I had before in my answer, you won't need it according to your question as it is now:
// create a separate group for each unique date and recordId
.GroupBy (m => m.date, m => m.recordId)
.OrderByDescending (m => m.Key)

This seems very similar to your other question - Reading a delimted file using LINQ
I don't believe you want to use Group here at all - I believe instead that you want to use OrderBy and ThenBy - something like:
var recipients = File.ReadAllLines(path)
.Select (record => record.Split('|'))
.Select (tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
recordId = tokens[13],
date = Convert.ToDateTime(tokens[17])
}
)
.OrderBy (m => m.recordId)
.ThenByDescending (m => m.date)
.Dump();
For a simple Take... you can just add this .Take(N) just before the Dump()
However, I'm not sure this is what you are looking for? Can you clarify your question?

just add
.OrderBy( g=> g.Key);
after your grouping. This will order your groupings by RecordId ascending.
Last, I want to .take(x) records where
x is dependent on some other factors.
Basically, the .take(x) will return
the most-recent x records.
If you mean by "the most recent" by date, why would you want to group by RecordId in the first place - just order by date descending:
..
.OrderByDescending (m => m.date)
.Take(x)
.Dump();
If you just want to get the top x records in the order established by the grouping though you could do the following:
...
.GroupBy (m => m.recordId)
.SelectMany(s => s)
.Take(x)
.Dump();

If you want something like the first 3 for each group, then I think you need to use a nested query like:
var recipients = File.ReadAllLines(path)
.Select(record => record.Split('|'))
.Select(tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
RecordId = tokens[13],
Date = Convert.ToDateTime(tokens[17])
}
)
.GroupBy(m => m.RecordId)
.Select(grouped => new
{
Id = grouped.Key,
First3 = grouped.OrderByDescending(x => x.Date).Take(3)
}
.Dump();
and if you want this flattened into a record list then you can use SelectMany:
var recipients = var recipients = File.ReadAllLines(path)
.Select(record => record.Split('|'))
.Select(tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
RecordId = tokens[13],
Date = Convert.ToDateTime(tokens[17])
}
)
.GroupBy(m => m.RecordId)
.Select(grouped => grouped.OrderByDescending(x => x.Date).Take(3))
.SelectMany(item => item)
.Dump();