LINQ return type for nested group query

I have the following query working in my code and now want to move into a separate class as a method that I call with List<Logrecord>, but having trouble determining what TYPE I need to return from the method.

recsByDate is a List<LogRecord> where records have Date, Time, EventType fields etc.

var vehicleGroupedByDate = from daterecs in recsByDate
where daterecs.Event == "Detection"
orderby daterecs.Date
group daterecs by daterecs.Date into vrecs
from vrecs2 in
(
from daterecs in vrecs
orderby daterecs.Time
group daterecs by daterecs.Vehicle
)
group vrecs2 by vrecs.Key;

Changed to type as you suggest and get error

Severity Code Description Project File Line Suppression State
Error CS0266 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>' to 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, System.Collections.Generic.List<BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>>'. An explicit conversion exists (are you missing a cast?)

public IEnumerable<IGrouping<DateTime, IGrouping<string, List<BodyGuardUserFriendlyLogRecord>>>>
GetVehicleDetections(List<BodyGuardUserFriendlyLogRecord> recsByDate)
{
var vehicleQuery = from daterecs in recsByDate
where daterecs.Event == "Detection"
orderby daterecs.Date
group daterecs by daterecs.Date into vrecs
from vrecs2 in
(
from daterecs in vrecs
orderby daterecs.Time
group daterecs by daterecs.Vehicle
)
group vrecs2 by vrecs.Key;
return vehicleQuery;
}

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LVL 13

louisfrCommented: 2016-08-07

You can find what the type of vehicleGroupedByDate is by hovering the mouse over the 'var' keyword.
Assuming that Date's type is DateTime and Vehicle's type is String, it should be:
IGrouping<DateTime, IGrouping<string, LogRecord>>

LVL 1

David HuismanAuthor Commented: 2016-08-08

I tried using the suggested return type and get error

Error CS0266 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>' to 'System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, System.Collections.Generic.List<BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>'. An explicit conversion exists (are you missing a cast?)

public IGrouping<DateTime, IGrouping<string, List<BodyGuardUserFriendlyLogRecord>>> GetVehicleDetections(List<BodyGuardUserFriendlyLogRecord> recsByDate)
{
var vehicleQuery = from daterecs in recsByDate
where daterecs.Event == "Detection"
orderby daterecs.Date
group daterecs by daterecs.Date into vrecs
from vrecs2 in
(
from daterecs in vrecs
orderby daterecs.Time
group daterecs by daterecs.Vehicle
)
group vrecs2 by vrecs.Key;

return vehicleQuery;
}

louisfrCommented: 2016-08-08

The error message gave you the type you were looking for:
IEnumerable<IGrouping<DateTime, IGrouping<string, List<BodyGuardUserFriendlyLogRecord>>>>

When I tried it, I checked only the items type, so the IEnumerable was missing.

My fault. Should copy/paste instead of retyping.
Sorry.
The error message gives you the right type.

System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>

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David HuismanAuthor Commented: 2016-08-21

Thanks for your help

LINQ return type for nested group query

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