I'm new to LINQ and I'm trying to group a list by two columns and use the count aggregate function but I'm not sure how to write this query properly.
Here is my class
public class Result
{
public string? Type { get; set; }
public int Age { get; set; }
public string? Name { get; set; }
public string? Description { get; set; }
public int Count { get; set; }
}
First I read some data from a dataTable and add it to a list of Result without Count property
List<Result> list = new();
foreach (DataRow row in dataTable.Rows)
{
list.Add(new Result
{
Type =row["Type"].ToString(),
Age = int.Parse(row["Age"].ToString()),
Name = row["Name"].ToString(),
Description = row["Description"].ToString(),
});
}
Now I want to group by Age and Type, I wrote this query and it returns the right result but I'm wondering if there is another cleaner way to write this instead of using Select().FirstOrDefault() ?
IEnumerable<Result> myResult = list.GroupBy(x => new { x.Age, x.Type }).Select(gr =>
new Result
{
Age = gr.Key.Age,
Type = gr.Key.Type,
Name = gr.Select(x => x.Name).FirstOrDefault(),
Description = gr.Select(x => x.Description).FirstOrDefault(),
Count = gr.Count()
}).ToList();
You can try to use FirstOrDefault()?. to make it simple which use Null-conditional
IEnumerable<Result> myResult = list.GroupBy(x => new { x.Age, x.Type }).Select(gr =>
new Result
{
Age = gr.Key.Age,
Type = gr.Key.Type,
Name = gr.FirstOrDefault()?.Name,
Description = gr.FirstOrDefault()?.Description,
Count = gr.Count()
}).ToList();
Related
I am looking for a way of optimizing my LINQ query.
Classes:
public class OffersObject
{
public List<SingleFlight> Flights { get; set; }
public List<Offer> Offers { get; set; } = new List<Offer>();
}
public class SingleFlight
{
public int Id { get; set; }
public string CarrierCode { get; set; }
public string FlightNumber { get; set; }
}
public class Offer
{
public int ProfileId { get; set; }
public List<ExtraOffer> ExtraOffers { get; set; } = new List<ExtraOffer>();
}
public class ExtraOffer
{
public List<int> Flights { get; set; }
public string Name { get; set; }
}
Sample object:
var sampleObject = new OffersObject
{
Flights = new List<SingleFlight>
{
new SingleFlight
{
Id = 1,
CarrierCode = "KL",
FlightNumber = "1"
},
new SingleFlight
{
Id = 2,
CarrierCode = "KL",
FlightNumber = "2"
}
},
Offers = new List<Offer>
{
new Offer
{
ProfileId = 41,
ExtraOffers = new List<ExtraOffer>
{
new ExtraOffer
{
Flights = new List<int>{1},
Name = "TEST"
},
new ExtraOffer
{
Flights = new List<int>{2},
Name = "TEST"
},
new ExtraOffer
{
Flights = new List<int>{1,2},
Name = "TEST"
}
}
}
}
};
Goal of LINQ query:
List of:
{ int ProfileId, string CommercialName, List<string> fullFlightNumbers }
FullFlightNumber should by created by "Id association" of a flight. It is created like: {CarrierCode} {FlightNumber}
What I have so far (works correctly, but not the fastest way I guess):
var result = sampleObject.Offers
.SelectMany(x => x.ExtraOffers,
(a, b) => {
return new
{
ProfileId = a.ProfileId,
Name = b.Name,
FullFlightNumbers = b.Flights.Select(f => $"{sampleObject.Flights.FirstOrDefault(fl => fl.Id == f).CarrierCode} {sampleObject.Flights.First(fl => fl.Id == f).FlightNumber}").ToList()
};
})
.ToList();
Final note
The part that looks wrong to me is:
.Select(f => $"{sampleObject.Flights.FirstOrDefault(fl => fl.Id == f)?.CarrierCode} {sampleObject.Flights.FirstOrDefault(fl => fl.Id == f)?.FlightNumber}").ToList()
I am basically looking for a way of "joining" those two lists of the OffersObject by Flight's Id.
Any tips appreciated.
If there will only be a few flights defined in sampleObject.Flights, a sequential search using a numeric key is hard to beat.
However, if the number of flights times the number of offers is substantial (1000s or more), I would suggest loading the list of flights into a dictionary with Id as the key for efficient lookup. Something like:
var flightLookup = sampleObject.Flights.ToDictionary(f => f.Id);
And then calculate your FullFlightNumbers as
FullFlightNumbers = b.Flights
.Select(flightId => {
flightLookup.TryGetValue(flightId, out SingleFlight flight);
return $"{flight?.CarrierCode} {flight?.FlightNumber}";
})
.ToList()
TryGetValue above will quietly return a null value for flight if no match is found. If you know that a match will always be present, the lookup cold alternately be coded as:
SingleFlight flight = flightLookup[flightId];
The above also uses a statement lambda. In short, lambda functions can have either expression or statement blocks as bodies. See the C# reference for more information.
I'd suggest replacing the double .FirstOrDefault() approach with .IntersectBy(). It is available in the System.Linq namespace, starting from .NET 6.
.IntersectBy() basically filters sampleObject.Flights by matching the flight ID for each flight in sampleObject with flight IDs in ExtraOffers.Flights.
In the code below, fl => fl.Id is the key selector for sampleObject.Flights (i.e. fl is a SingleFlight).
var result = sampleObject.Offers
.SelectMany(x => x.ExtraOffers,
(a, b) => {
return new
{
ProfileId = a.ProfileId,
Name = b.Name,
FullFlightNumbers = sampleObject.Flights
.IntersectBy(b.Flights, fl => fl.Id)
.Select(fl => fl.FullFlightNumber) // alternative 1
//.Select(fl => $"{fl.CarrierCode} {fl.FlightNumber}") // alternative 2
.ToList()
};
})
.ToList();
In my suggestion I have added the property FullFlightNumber to SingleFlight so that the Linq statement looks slightly cleaner:
public class SingleFlight
{
public int Id { get; set; }
public string CarrierCode { get; set; }
public string FlightNumber { get; set; }
public string FullFlightNumber => $"{CarrierCode} {FlightNumber}";
}
If defining SingleFlight.FullFlightNumber is not possible/desirable for you, the second alternative in the code suggestion can be used instead.
Example fiddle here.
I have the following query in linq, which takes 2 lists as a data source. The first contains a list of ProductID and its description
public class Venta
{
public string ProductoId { get; set; }
public string clienteRut { get; set; }
}
public class Ventas
{
public List<Venta> lstVentas { get; set; }
}
and the other list has the products sold
public class Productos
{
public List<Producto> lstProductos { get; set; }
}
public class Producto
{
public string id { get; set; }
public string name { get; set; }
}
I need to consult the 5 most sold products, ordered by quantity from the most sold, to the least sold.
So far I have the following linq query, but I do not know how to do it so that I am given the list of the first 5, ordered from highest to lowest based on the quantity (cont)
Venta vta1 = new Venta();
vta1.ProductoId = "1";
vta1.clienteRut = "121370654";
Venta vta2 = new Venta();
vta2.ProductoId = "2";
vta2.clienteRut = "121370654";
Venta vta3 = new Venta();
vta3.ProductoId = "3";
vta3.clienteRut = "121370654";
List<Venta> lstVentasDia = new List<Venta>();
lstVentasDia.Add(vta1);
lstVentasDia.Add(vta2);
lstVentasDia.Add(vta3);
VentasDia vtas = new VentasDia();
vtas.date = "2018-05-01";
vtas.lstVentas = lstVentasDia;
var Lista5Top = from vendidos in vtas.lstVentas
orderby vendidos.ProductoId
group vendidos by vendidos.ProductoId into Grupo
select new { key = Grupo.Key, cont = Grupo.Count() };
I need in addition to that group of result, add the name of the product that is in the list Products, and order it by quantity sold of greater to less only the first 5
Thankful in advance
Gloria
Try following :
Productos productos = new Productos();
var Lista5Top = (from vendidos in vtas.lstVentas
join prod in productos.lstProductos on vendidos.ProductoId equals prod.id
select new { id = vendidos.ProductoId, rut = vendidos.clienteRut, name = prod.name })
.OrderBy(x => x.id)
.GroupBy(x => x.id)
.Select(x => new { id = x.Key, cont = x.Count(), name = x.FirstOrDefault().name })
.OrderByDescending(x => x.cont)
.Take(5).ToList();
I have an IEnumerable<ValueObj> object with multiple valid ValueObj objects in it. I would like to group those objects by Id and receive Dictionary<Guid, IEnumerable<ValueObj>> where the Key is Id from ValueObj, and Value is just unchanged ValueObj.
public class ValueObj
{
public Guid Id { get; set; }
public string Name { get; set; }
public DateTime Time { get; set; }
public double Result { get; set; }
}
I've tried to mess with Linq GroupBy but with no success
IEnumerable<ValueObj> persons = ...;
var results = persons.GroupBy(
p => p.Id,
p => p,
(key, g) => new { PersonId = key, Cars = g.ToList() });
Try this:
IEnumerable<ValueObj> col = ...;
var dict = col.GroupBy(x => x.Id).ToDictionary(x => x.Key, x => x.ToList());
I got this LinQ statement
var daysList = new List<int>(new int[30]);
var model_pdv = db_pdv.Pdv.GroupBy(x => new { Pdv = x.Clave_PDV, Nombre_Pdv = x.Nombre_Pdv})
.Select(x => new DishVM()
{
Clave_PDV = x.Key.Pdv,
Nombre_Pdv = x.Key.Nombre_Pdv,
Days = daysList,
Data = x
}).ToList();
However i dont know why my "Data" List inside my LinQ gets empty values the first time but then i saves the LinQ as it should
This is my DishVm Class:
public class DishVM
{
public string Clave_PDV { get; set; }
public string Nombre_Pdv { get; set; }
public IEnumerable<Pdv> Data { get; set; }
}
And my Pdv class:
public class Pdv
{
public string Clave_PDV { get; set; }
public string Nombre_Pdv { get; set; }
}
How can i avoid the empty Data List?
The type of x within your Select statement is IGrouping, change it to produce a list:
var model_pdv = db_pdv.Pdv.GroupBy(x => new { Pdv = x.Clave_PDV, Nombre_Pdv = x.Nombre_Pdv})
.Select(x => new DishVM()
{
Clave_PDV = x.Key.Pdv,
Nombre_Pdv = x.Key.Nombre_Pdv,
Days = daysList,
Data = x.ToList()
}).ToList();
Hello all what is wrong with my GroupBy query ?
I have following class:
public class AssembledPartsDTO
{
public int PID { get; set; }
public McPosition Posiotion { get; set; }
public string Partnumber { get; set; }
public string ReelID { get; set; }
public int BlockId { get; set; }
public List<string> References { get; set; }
}
I am trying to perform following query:
assembledPcb.AssembledParts.GroupBy(entry => new
{
entry.PID,
entry.Posiotion.Station,
entry.Posiotion.Slot,
entry.Posiotion.Subslot,
entry.Partnumber,
entry.ReelID,
entry.BlockId
}).
Select( (key , val )=> new AssembledPartsDTO
{
BlockId = key.Key.BlockId,
PID = key.Key.PID,
Partnumber = key.Key.Partnumber,
ReelID = key.Key.ReelID,
Posiotion = new McPosition(key.Key.Station, key.Key.Slot, key.Key.Subslot),
References = val <-- ????
})
But the val that I have there is of type int and not the val of grouping that I can do there val.SelectMany(v => v).ToList(); any idea what is wrong in my code ?
The second parameter of Enumerable.Select is the index of the item in the sequence. So in this case it is the (zero based) number of the group. You just want to select the group, you don't need it's index:
var result = assembledPcb.AssembledParts.GroupBy(entry => new
{
entry.PID,
entry.Posiotion.Station,
entry.Posiotion.Slot,
entry.Posiotion.Subslot,
entry.Partnumber,
entry.ReelID,
entry.BlockId
})
.Select(g => new AssembledPartsDTO
{
BlockId = g.Key.BlockId,
PID = g.Key.PID,
Partnumber = g.Key.Partnumber,
ReelID = g.Key.ReelID,
Posiotion = new McPosition(g.Key.Station, g.Key.Slot, g.Key.Subslot),
References = g.SelectMany(entry => entry.References)
.Distinct()
.ToList()
});
(assuming that you want a list of distinct references)
Side-Note: you have a typo at the property-name: Posiotion