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Query with Linq and count matches in the Where clause and project it

Need to query many columns for possible matches and then see how many did match and add that to a column in the Select projection. I could have two column of the four match but how many did? Then want to sort the result by how many matches. Do I need to group them first? Do a separate aggregation? Kind of stumped as which way to go because the real one would have a lot more tests of fields in production. Could possibly match as many as 8 tests in the where clause.
var results = _RList
.Where(d => d.RMI15Min == RMI.ConfirmedBottom || d.RMI15Min == RMI.InPlaceBottomConfirmed
|| d.RMI30Min == RMI.ConfirmedBottom || d.RMI30Min == RMI.InPlaceBottomConfirmed)
.OrderBy(d => d.Instrument)
.Select(d => new
{
d.Instrument,
d.Description,
d.RMI15Min,
d.RMI30Min,
NewColumn with the total of the matches in the .Where clause above.
}).ToList();

Assuming _RList does not tie back to a database table
var confirmedList = new List<int> { RMI.ConfirmedBottom, RMI.InPlaceBottomConfirmed };
var results = _RList
.OrderBy(d => d.Instrument)
.Select(d => new
{
d.Instrument,
d.Description,
d.RMI15Min,
d.RMI30Min,
Count = (new List<int> { d.RMI15Min, d.RMI30Min }).Count(c => confirmedList.Contains(c))
})
.Where(d => d.Count > 0)
.ToList();
If it ties back to a database table, it depends on whether your library can convert the above LINQ statement.

I would consider using ternary operators to add 1/0 to the total;
Count = (d.RMI15Min == RMI.ConfirmedBottom ? 1 : 0)
+ (d.RMI15Min == RMI.InPlaceBottomConfirmed ? 1 : 0)
+ (d.RMI30Min == RMI.ConfirmedBottom ? 1 : 0)
+ (d.RMI30Min == RMI.InPlaceBottomConfirmed ? 1 : 0)
Then filter the list after calculating the count.

Getting the count of most repeated records in Linq

I am working on an application in which I have to store play history of a song in the data table. I have a table named PlayHistory which has four columns.
Id | SoundRecordingId(FK) | UserId(FK) | DateTime
Now i have to implement a query that will return the songs that are in trending phase i.e. being mostly played. I have written the following query in sql server that returns me data somehow closer to what I want.
select COUNT(*) as High,SoundRecordingId
from PlayHistory
where DateTime >= GETDATE()-30
group by SoundRecordingId
Having COUNT(*) > 1
order by SoundRecordingId desc
It returned me following data:
High SoundRecordingId
2 5
2 3
Which means Song with Ids 5 and 3 were played the most number of times i.e.2
How can I implement this through Linq in c#.
I have done this so far:
DateTime d = DateTime.Now;
var monthBefore = d.AddMonths(-1);
var list =
_db.PlayHistories
.OrderByDescending(x=>x.SoundRecordingId)
.Where(t => t.DateTime >= monthBefore)
.GroupBy(x=>x.SoundRecordingId)
.Take(20)
.ToList();
It returns me list of whole table with the count of SoundRecording objects but i want just count of the most repeated records.
Thanks

There is an overload of the .GroupBy method which will solve your problem.
DateTime d = DateTime.Now;
var monthBefore = d.AddMonths(-1);
var list =
_db.PlayHistories
.OrderByDescending(x=>x.SoundRecordingId)
.Where(t => t.DateTime >= monthBefore)
.GroupBy(x=>x.SoundRecordingId, (key,values) => new {SoundRecordingID=key, High=values.count()})
.Take(20)
.ToList();
I have simply added the result selector to the GroupBy method call here which does the same transformation you have written in your SQL.
The method overload in question is documented here
To go further into your problem, you will probably want to do another OrderByDescending to get your results in popularity order. To match the SQL statement you also have to filter for only counts > 1.
DateTime d = DateTime.Now;
var monthBefore = d.AddMonths(-1);
var list =
_db.PlayHistories
.Where(t => t.DateTime >= monthBefore)
.GroupBy(x=>x.SoundRecordingId, (key,values) => new {SoundRecordingID=key, High=values.count()})
.Where(x=>x.High>1)
.OrderByDescending(x=>x.High)
.ToList();

I like the 'linq' syntax it's similar to SQL
var query = from history in _db.PlayHistories
where history.DateTime >= monthBefore
group history by history.SoundRecordingId into historyGroup
where historyGroup.Count() > 1
orderby historyGroup.Key
select new { High = historyGroup.Count(), SoundRecordingId = historyGroup.Key };
var data = query.Take(20).ToList();

You´re allmost done. Just order your list by the count and take the first:
var max =
_db.PlayHistories
.OrderByDescending(x=>x.SoundRecordingId)
.Where(t => t.DateTime >= monthBefore)
.GroupBy(x=>x.SoundRecordingId)
.OrderByDescending(x => x.Count())
.First();
This gives you a single key-value-pair where the Key is your SoundRecordingId and the value is the number of its occurences in your input-list.
EDIT: To get all records with that amount chose this instead:
var grouped =
_db.PlayHistories
.OrderByDescending(x => x.SoundRecordingId)
.Where(t => t.DateTime >= monthBefore)
.GroupBy(x => x.SoundRecordingId)
.Select(x => new { Id = x.Key, Count = x.Count() }
.OrderByDescending(x => x.Count)
.ToList();
var maxCount = grouped.First().Count;
var result = grouped.Where(x => x.Count == maxCount);

This solves the problem by giving you what you asked for. Your query in LINQ, returning just the play counts.
var list = _db.PlayHistories.Where(x => x.DateTimeProp > (DateTime.Now).AddMonths(-1))
.OrderByDescending(y => y.SoundRecordingId.Count())
.ThenBy(z => z.SoundRecordingId)
.Select(xx => xx.SoundRecordingId).Take(20).ToList();

Determine Duplicate data using LINQ to EF

I have a dataset that i want to groupby to determine duplicate data.
Example i have a dataset that looks like this.
|id | Number | ContactID
1 1234 5
2 9873 6
3 1234 7
4 9873 6
Now i want to select data that has more than one occurrence of Number but only if the ContactID is not the same.
So basically return
| Number | Count |
1234 2
Any help would be appreciated using LINQ to EF, thanks.

Update:
All thanks to #DrCopyPaste, as he told me that I misunderstood your problem. Here is the correct solution:-
var result = from c in db.list
group c by c.Number into g
let count = g.GroupBy(x => x.ContactID).Where(x => x.Count() == 1).Count()
where count != 0
select new
{
Number = g.Key,
Count = count
};
Sample Fiddle.

This query avoids making a custom IEqualityComparer as if I remember correctly don't think they play well with EF.
var results = data.GroupBy(number => number.Number)
.Where(number => number.Count() > 1)
.Select(number => new
{
Number = number.Key,
Count = number.GroupBy(contactId => contactId.ContactId).Count(x => x.Count() == 1)
})
.Where(x => x.Count > 0).ToList();
Fiddle
It does an initial GroupBy to get all Numbers that are duplicated. It then selects a new type that contains the number and a second GroupBy that groups by ContactId then counts all groups with exactly one entry. Then it takes all results whose count is greater than zero.
Have not testing it against EF, but the query uses only standard Linq operators so EF shouldn't have any issues translating it.

Another way of doing this(using 1 level of grouping):
var results = data
.Where(x => data.Any(y => y.Id != x.Id && y.Number == x.Number && y.ContactId != x.ContactId))
.GroupBy(x => x.Number)
.Select(grp => new { Number = grp.Key, Count = grp.Count() })
.ToList();
Fiddle

'int' does not contain a definition for 'ToList'

So I'm trying to run a Linq query that's analogous to the SQL query:
SELECT COUNT(*)
FROM table
WHERE ww >= [wwStartSelected]
AND ww <= [wwEndSelected]
AND manager='[managerName]'
AND status='Done'
GROUP BY ww;
To get a count of the number of rows (tasks) within the given ww range that are marked as done under a particular manager and grouped by ww. I've tried to create a LINQ query that would return something similar (wwStartSelected && wwEndSelected are global vars):
protected List<int> getManagerDoneCount(string managerName)
{
using (var context = new InfoDBContext())
{
List<int> managerDoneCount = context.InfoSet.Where(x => x.ww >= wwStartSelected && x.ww <= wwEndSelected && x.manager == managerName && x.status == "Done").GroupBy(x => x.ww).Count().ToList();
return managerDoneCount;
}
}
This query would then feed into a chart:
var testChart = new Chart(width: 600, height: 400)
.AddTitle("Test")
.AddSeries(
name: "Done",
chartType: "StackedColumn100",
xValue: new[] { WWList },
yValues: new[] { getManagerDoneCount("someManager") })
However I'm running into an issue with my Linq line and it says:
'int' does not contain a definition for 'ToList' and no extension method 'ToList'
accepting a first argument of type 'int' could be found (are you
missing a using directive or an assembly reference?)
Is there way to get fix this easily or do I have to convert to string, then convert back to int for the chart series (the latter of which seems a bit silly [but if so, best way to do so])?

.Count().ToList()
You're asking it to count the items in the list (which results in a number) and then convert that single number into a list, which makes no sense.
Either return a list and count it later (omit the .Count()) or, change the method to return an int not a List<int> and omit the .ToList()
protected int getManagerDoneCount(string managerName)
{
using (var context = new InfoDBContext())
{
int managerDoneCount = context.InfoSet
.Where(x => x.ww >= wwStartSelected &&
x.ww <= wwEndSelected &&
x.manager == managerName &&
x.status == "Done")
.GroupBy(x => x.ww)
.Count();
return managerDoneCount;
}
}
As an aside, to save you writing hundreds of these methods, you can pass the Where clause in as a parameter...
using System.Linq.Expressions;
protected int getManagerCount(string managerName, Expression<Info> predicate)
{
using (var context = new InfoDBContext())
{
int managerDoneCount = context.InfoSet
.Where(predicate)
.GroupBy(x => x.ww)
.Count();
return managerDoneCount;
}
}
Then call it like this...
var count = getManagerCount("...", x => x.ww >= wwStartSelected &&
x.ww <= wwEndSelected &&
x.manager == managerName &&
x.status == "Done");
Edit Re: Comments
To return a count of each group, List<int> is a bad idea as you aren't ordering the groups so the counts will be in an undefined order. The ideal solution is to have a class that has an appropriate Key and Count property, but to simplify the example, I'll use a Tuple.
//I'm assuming `ww` is an `int`, change the first type parameter of the tuple as appropriate
List<Tuple<int, int>> counts = context.InfoSet
.Where(x => x.ww >= wwStartSelected &&
x.ww <= wwEndSelected &&
x.manager == managerName &&
x.status == "Done")
.GroupBy(x => x.ww)
.Select(x => new Tuple<int, int>(x.Key, x.Count())).ToList();
Note that after you've done the group, the next Select is against the group, which has a Key property for the thing you've grouped on and a lot of aggregate methods for counting, summing, etc..
If you really just want a list of ints, change the last Select to be...
.Select(x => x.Count())
If you weren't passing it out of the method, I'd just use an anonymous class...
.Select(x => new {Ww = x.Key, Count = x.Count()})
But that's no use in a method signature. If you created a CountResult class with Ww and Count properties...
.Select(x => new CountResult{Ww = x.Key, Count = x.Count()})
Edit Re: Comments #2
Linq-To-Entities builds an expression tree which is executed against SQL server, whereas Linq-To-Objects runs in-memory on the client and has more features (as it doesn't need to work out equivalent SQL). In this case, when it gets results from SQL it creates a special proxy class that looks/behaves the same as your entities but handle additional things like tracking which properties have changed. Because of this, you can only use classes which can be constructed (with a parameterless constructor) and then have their properties set (and tracked).
(Although you didn't specify Linq-To-Entities, it's obvious from your question so I should've caught this).
LINQ doesn't deal in lists, but IQueryables, which support lazy evaluation.
Eg If you do...
var a = dbcontext.SomeSet.Where(x => true); //You could omit the Where entirely, just for illustration purposes
var b = a.Where(x => x.Id < 100);
var c = b.ToList();
The query is only executed on the last line and at most 100 records will be returned by the database. a and b are both IQueryable<SomeSet> and "just" contain the expression tree (basically a hierarchy representing the constrains/operations applied so far).
So, to be able to use parameterised constructors / other Linq-To-Object features, we can force the evaluation ...
List<Tuple<int, int>> counts = context.InfoSet
.Where(x => x.ww >= wwStartSelected &&
x.ww <= wwEndSelected &&
x.manager == managerName &&
x.status == "Done")
.GroupBy(x => x.ww)
.ToList() // <<<< Force execution of SQL query
.Select(x => new Tuple<int, int>(x.Key, x.Count())).ToList();
Which should allow you to use constructors, should you wish.
That said, getting a zero count is difficult - the same as it would be getting it from a database (if you group by a field, it doesn't show any 0 counts). There are a number of ways to approach this and which one you use depends on how much data you're playing with. All of them require some way of defining all possible values. I'll use a List<string> as it works well with LINQ
You could, for example get a list of all values and run a different count for each. This is easy but requires multiple queries. If there are lots of groups, it might be expensive...
var groups = new List<string> {"ww1", "ww2", ...};
var counts = groups.Select(g => context.InfoSet.Where(x => x.ww == g &&
x.manager == managerName &&
x.status == "Done").Count());
(This will only return counts, but in the same order as your groups list. As before, you can Select anything you like, including a CountResult...)
var counts = groups.Select(g => new CountResult {
Ww = g,
Count = context.InfoSet.Where(x => x.ww == g &&
x.manager == managerName &&
x.status == "Done").Count();
});
Alternatively, you can run the query you were doing previously and add the missing groups with a count of 0. This has the benefit of running a single SQL query and letting the database do all the heavy lifting (Ok, handling a few counts isn't too expensive but it's worth bearing in mind for other problems - you don't want to get the whole DB table in memory and do the processing there!).
var groups = new List<string> {"ww1", "ww2", ...};
var previousQuery = ... //(I'll assume a List<CountResult> but tuple would work the same)
var finalList = previousQuery.Concat(
groups.Where(g => ! previousQuery.Exists(p => p.Ww == g))
.Select(g => new CountResult {Ww=g, Count=0})
);
In short, take the previous results set, and concatenate (join) it with the result of; (take a list of all groups, remove those already in set 1, for the remainder create a new object with the appropriate ww and a count of 0)

C# Retrieve Common Records by LINQ

I have a database with the table that keeps user_ids and tag_ids. I want to write a function which takes two user_ids and returns the tag_ids that both users have in common.
These are the sample rows from the database:
User_id Tag_id
1 100
1 101
2 100
3 100
3 101
3 102
What I want from my function is that when I call my function like getCommonTagIDs(1, 3), it should return (100,101). What I did so far is that I keep the rows which are related to user_id in two different lists and then using for loops, return the common tag_ids.
using (TwitterDataContext database = TwitterDataContext.CreateTwitterDataContextWithNoLock())
{
IEnumerable<Usr_Tag> tags_1 = database.Usr_Tags.Where(u => u.User_id == userID1).ToList();
IEnumerable<Usr_Tag> tags_2 = database.Usr_Tags.Where(u => u.User_id == userID2).ToList();
foreach (var x in tags_1)
{
foreach (var y in tags_2) {
if (x.Tag_id == y.Tag_id) {
var a =database.Hashtags.Where(u => u.Tag_id==x.Tag_id).SingleOrDefault();
Console.WriteLine(a.Tag_val);
}
}
}
}
What I want to ask is that, instead of getting all rows from database and searching for the common tag_ids in the function, I want to get the common tag_ids directly from database with LINQ by making the calculations on the database side. I would be grateful if you could help me.
This is the SQL that I wrote:
SELECT [Tag_id]
FROM [BitirME].[dbo].[User_Tag]
WHERE USER_ID = '1' AND Tag_id IN (
SELECT [Tag_id]
FROM [BitirME].[dbo].[User_Tag]
where USER_ID = '3')

What you want is the "Intersection" of those two sets:
var commonTags = database.Usr_Tags.Where(u => u.User_id == userID1).Select(u => u.Tag_id)
.Intersect(database.Usr_Tags.Where(u => u.User_id == userID2).Select(u => u.Tag_id));
And voila, you're done.
Or, to clean it up a bit:
public static IQueryable<int> GetUserTags(int userId)
{
return database.Usr_Tags
.Where(u => u.User_id == userId)
.Select(u => u.Tag_id);
}
var commonTags = GetUserTags(userID1).Intersect(GetUserTags(userID2));

Here's one way to do it:
int[] users = new int[] {1,3}; // for testing
database.Ustr_Tags.Where(t => users.Contains(t.User_id))
.GroupBy(t => t.Tag_id)
.Where(g => users.All(u => g.Any(gg=>gg.User_id == u))) // all tags where all required users are tagged
.Select(g => g.Key);
One benefit of this one is it can be used for any number of users (not just 2).

If i got it right, query like this is maybe what you need
var q = from t in database.Usr_Tags
//all Usr_Tags for UserID1
where t.User_Id == userID1 &&
//and there is a User_tag for User_ID2 with same Tag_ID
database.User_Tags.Any(t2=>t2.User_ID==userID2 && t2.Tag_ID==t.Tag_ID)
select t.Tag_Id;
var commonTags = q.ToList();