How should I structure a Linq query to return a List or Ienumerable of the most popular Tags in my db (I am using EF4.1 by the way).
Currently I have:
var tagsListing = db.Tags
.GroupBy(q => q.Name)
.OrderByDescending(gp => gp.Count())
.Take(5)
.Select();
I think I am part of the way there, but I am unsure of how to structure the Select statement...
Your Select call could look like this:
.Select(gp => gp.Key)
That will give you an IEnumerable<string> of your most popular tags (assuming that Name is a string).
Assuming you want the name and the count, just:
.Select(g => new { Name = g.Key, Count = g.Count() });
EDIT: If you want the complete tags as well, you could use:
.Select(g => new { Tags = g, Count = g.Count() })
which would give you a sequence of groups of tags, all with the same name within a group. Or you might only want the first tag within each group, e.g.
.Select(g => g.First())
It's not clear what a Tag consists of, or what exactly you want in the results.
You've written a perfectly workable query and do not need to call .Select
IQueryable<IGrouping<string, Tag>> tagsListing = db.Tags
.GroupBy(q => q.Name)
.OrderByDescending(gp => gp.Count())
.Take(5);
List<IGrouping<string, Tag>> results = tagListing.ToList();
You probably want to select the names like this:
.Select(gp => gp.Key);
Related
My code is something like this:
List<int> IDs = new List<int> {9,7,38, 23}
IQueryable<Post> pp = myDataEntity.Posts.Where(p=>IDs.Contains(p.ID));
How can I explain that I want to sort pp by the order of ID in the IDs? Thank you.
You can order by List.IndexOf:
IQueryable<Post> orderedPosts myDataEntity.Posts
.Select(p => new { Post=p, Index=IDs.IndexOf(p.ID) })
.Where(x => x.Index >= 0)
.OrderBy(x => x.Index)
.Select(x => x.Post);
Assuming you want to keep the order of ID you have in IDs and not actually the ordered verison of it, this is how you can do it:
var pp = IDs.Select(x=> myDataEntity.Posts.Where(p=>p.ID == x))
.SelectMany(x=>x);
Using IDs as your external collection, you get to keep the ordering of the elements in it.
use OrderByDescending
IQueryable<Post> pp = myDataEntity.Posts.Where(p=>IDs.Contains(p.ID))
.OrderByDescending(p => p.ID)
I have an xml document
<NumSet>
<num>1</num>
<num>2</num>
<num>2</num>
<num>3</num>
</NumSet>
I want unique elements shown up, ie 1 and 3. not distinct which will also bring out 2.
How to do that? Do I have to use Group? Is there any concise way to do that?
You are right, you can use GroupBy and filter group which has only one item by using Count() == 1:
var output = XDocument.Load(xmlFile)
.Descendants("num")
.Select(e => e.Value)
.GroupBy(x => x)
.Where(g => g.Count() == 1)
.Select(g => g.Key);
It sounds like you want a Distinct GroupBy query... Take a look at the Need help on Linq with group by and distinct post here on StackOverflow.
XElement xe = XElement.Parse(#"<NumSet><num>1</num><num>2</num><num>2</num><num>3</num></NumSet>");
var query = xe.Elements("num")
.GroupBy(x => x.Value)
.Where(x=>x.Count ()==1)
.Select (x => x);
To do what you need I'd say that yes, you need to use GrouBy, and then count the elements in each group, and return those that contains just one element. In code, this translates to:
var query = lst.GroupBy(x => x)
.Where(x => x.Count() == 1)
.Select(x => x.Key);
I'm trying to add a column to the following LINQ expression. I want the column to contain a string concatenation of a text value in a many table called WasteItems. The join would be on "Waste.WasteId = WasteItem.WasteId". My problem is I need to display in a single dynamic column a string such as "EW (5); EX (3)" if there was 8 records in WasteItem and the column containing the 2 character string was called WasteItem.EWC. Hope that makes sense, there must be an efficient way since I realise LINQ is very powerfull. I'm new to it and not sure how to start or go about this:
return from waste in this._db.Wastes
where (from u in _db.UsersToSites.Where(p => p.UserId == userId && p.SystemTypeId == SystemType.W)
select u.SiteId)
.Contains(waste.SiteId)
orderby waste.Entered descending select waste;
THANKS IN ADVANCE
Something like this should do:
wastes.GroupJoin(db.WasteItems, w => w.WastId, wi => wi.WasteId, (w,wi) => new { w, wi })
.AsEnumerable()
.Select(x => new
{
x.w.Name,
Items = string.Join(", ", x.wi.GroupBy(wi => wi.EWC).Select(g => string.Format("{0} ({1})", g.Key, g.Count())))
})
Where wastes is the result from your query. The AsEnumerable() is necessary because Entity Framework can not handle string.Join, so that part must be dealt with in memory.
I could not check the syntax, obviously, but at least it may show you the way to go.
Currently, I have the following LINQ queries. How can I merge the two queries into one. Basically, write a LINQ query to bring back the results I'd get from
IEnumerable<int> deltaList = people2010.Except(allPeople);
except in a single query.
var people2010 = Contacts.Where(x => x.Contractors
.Any(d => d.ContractorsStatusTrackings
.Any(date => date.StatusDate.Year >= 2010)))
.Select(x => x.ContactID);
var allPeople = Contacts.Where(x => x.Contractors
.Any(m => m.ContactID == x.ContactID))
.Select(x=> x.ContactID);
Thanks!
Why can you not just do Except as you are doing? Don't forget that your people2010 and allPeople variables are just queries - they're not the data. Why not just use them as they are?
If that's not acceptable for some reason, please give us more information - such as whether this is in LINQ to Object, LINQ to SQL etc, and what's wrong with just using Except.
It sounds like you're just looking for a more elegant way to write your query. I believe that this is a more elegant way to write your combined queries:
var deltaList =
from contact in Contacts
let contractors = contact.Contractors
where contractors.Any(ctor => ctor.ContractorStatusTrackings
.Any(date => date.StatusDate.Year >= 2010))
&& !contractors.Any(m => m.ContactID == contact.ContactID)
select contact.ContactID
I am a newbie to Linq. I am trying to write a linq query to get a min value from a set of records. I need to use groupby, where , select and min function in the same query but i am having issues when using group by clause. here is the query I wrote
var data =newTrips.groupby (x => x.TripPath.TripPathLink.Link.Road.Name)
.Where(x => x.TripPath.PathNumber == pathnum)
.Select(x => x.TripPath.TripPathLink.Link.Speed).Min();
I am not able to use group by and where together it keeps giving error .
My query should
Select all the values.
filter it through the where clause (pathnum).
Groupby the road Name
finally get the min value.
can some one tell me what i am doing wrong and how to achieve the desired result.
Thanks,
Pawan
It's a little tricky not knowing the relationships between the data, but I think (without trying it) that this should give you want you want -- the minimum speed per road by name. Note that it will result in a collection of anonymous objects with Name and Speed properties.
var data = newTrips.Where(x => x.TripPath.PathNumber == pathnum)
.Select(x => x.TripPath.TripPathLink.Link)
.GroupBy(x => x.Road.Name)
.Select(g => new { Name = g.Key, Speed = g.Min(l => l.Speed) } );
Since I think you want the Trip which has the minimum speed, rather than the speed, and I'm assuming a different data structure, I'll add to tvanfosson's answer:
var pathnum = 1;
var trips = from trip in newTrips
where trip.TripPath.PathNumber == pathnum
group trip by trip.TripPath.TripPathLink.Link.Road.Name into g
let minSpeed = g.Min(t => t.TripPath.TripPathLink.Link.Speed)
select new {
Name = g.Key,
Trip = g.Single(t => t.TripPath.TripPathLink.Link.Speed == minSpeed) };
foreach (var t in trips)
{
Console.WriteLine("Name = {0}, TripId = {1}", t.Name, t.Trip.TripId);
}