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);
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)
Earlier I put a question on Stackoverflow about how to remove duplicate records in a list of objects, based on a particular property within each object.
I got the answer I was looking for (see below), a query which returns a distinct list of objects using MainHeadingID as the property to remove duplicates.
public IList<tblcours> GetAllCoursesByOrgID(int id)
{
return _UoW.tblcoursRepo.All.
Where(c => c.tblCourseCategoryLinks.Any(cl => cl.tblUnitCategory.tblUnit.ParentID == id))
.GroupBy(c => c.MainHeadingID)
.Select(g => g.FirstOrDefault())
.ToList();
}
However, now I need more help! Is there anyway of amending the query above so that, it only removes duplicate values when MainHeadingID is not equal to 180. I tried amending GroupBy line to
.GroupBy(c => c.MainHeadingID != 180)
However, this didn't work.
Any help would be much appreciated with this.
Thanks.
Following works for LINQ to SQL:
return _UoW.tblcoursRepo.All
.Where(c => c.tblCourseCategoryLinks.Any(cl => cl.tblUnitCategory.tblUnit.ParentID == id))
.GroupBy(c => c.MainHeadingID)
//.SelectMany(g => g.Key == 180 ? g : g.Take(1))
.SelectMany(g => g.Take(g.Key == 180 ? Int32.MaxValue : 1))
.ToList();
Comments: SelectMany in query above selects all items from group where MainHeadingID equals to 180, but it takes only one item form other groups (i.e. distinct result). Linq to SQL cannot translate commented out part, but thanks to #usr there is way around.
Linq to Entities cannot translate even simplified query. I think only option for you in this case is simple concating result of two queries:
Expression<Func<tblcours, bool>> predicate = x =>
x.tblCourseCategoryLinks.Any(cl => cl.tblUnitCategory.tblUnit.ParentID == id)
int headingId = 180;
return _UoW.tblcoursRepo.All
.Where(c => c.MainHeadingID != headingId)
.Where(predicate)
.GroupBy(c => c.MainHeadingID)
.Select(g => g.FirstOrDefault())
.Concat(_UoW.tblcoursRepo.All
.Where(c => c.MainHeadingID == headingId)
.Where(predicate))
.ToList();
lazyberezovsky's answer fails due to an EF bug (which is not surprising given the quality of EF's LINQ support). It can be made to work with a hack:
.SelectMany(g => g.Key == 180 ? g.Take(int.MaxValue) : g.Take(1))
or
.SelectMany(g => g.Take(g.Key == 180 ? int.MaxValue : 1))
Note that performance will not be particularly good due to the way this is translated to SQL.
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);
I am using "Linq" to filter list of objects and to sort them, like
myList.Where(x => x.Item!= "SF" && x.AdSize == minadSize)
.OrderBy(x => x.ManufacturingDate)
.OrderBy(x=>x.ExpiryDate);
I doubt whether i am doing it right or not that is if i want to "sorting" on multiple fields then is it necessary to use multiple Order By clause cant it be done with single "OrderBy"
Don't use multiple OrderBy calls - use OrderBy followed by ThenBy:
var query = myList.Where(x => x.Item!= "SF" && x.AdSize == minadSize)
.OrderBy(x => x.ManufacturingDate)
.ThenBy(x => x.ExpiryDate); // Could add more ThenBy calls
If you use OrderBy twice, it will reorder the already-ordered-by-date list by expiry-date, whereas I assume you only want to order by expiry date for items with an equal manufacturing date, which is what the above does.
Obviously there's a ThenByDescending method too. For example:
var query = people.OrderBy(x => x.LastName)
.ThenBy(x => x.FirstName)
.ThenByDescending(x => x.Age)
.ThenBy(x => x.SocialSecurity);
I have a linq expression that returns transactions in groups. Each transaction has a numerical value and I now need to know what is the highest value from all the transactions returned. This value is held in a field called TransactionId
Here is the expression I am using to get the grouped list.
var transactions = ctx.MyTransactions
.Where (x => x.AdapterId == Id)
.GroupBy(x => x.DeviceTypeId);
I now need to write an expression that works on the “transactions” grouped list to find the “max” of the TransactionId field. I’ve tried different ideas but none seem to work with the grouped results. I’m new to linq so I’m not sure how to do this.
Have you tried finding the maximum in each group and then finding the maximum of that over all groups?
int max = transactions.Max(g => g.Max(t => t.TransactionId));
Or you could just query the database again:
int max = ctx.MyTransactions
.Where(x => x.AdapterId == Id)
.Max(t => t.TransactionId);
This will give you the max in each group
var transactionIds = ctx.MyTransactions
.Where (x => x.AdapterId == Id)
.GroupBy(x => x.DeviceTypeId,
g => new {
DeviceTypeId = g.Key,
MaxTransaction = g.Max(x => x.TransactionId)
});