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Using Linq to look for gap in dates

I have a single queryable that is ordered by id and then by date in descending order (most recent will appear first), tracking when the item (id) was online. If a gap is detected (more than 1 day) I want to filter out all of the dates that come prior to the gap, as to only get the most recent range of online days.
Currently I am looping through with for loops, however the data set is very large so I would like to improve performance using linq.
Are there any ways to compare the records by id, then date, and remove elements of that id after a gap is detected ( current.date - next.date != 1)?
Id
Date
1
2022/01/01
1
2021/12/31
1
2021/12/25
2
2021/12/20
2
2021/12/19
2
2021/12/18
2
2021/12/15
would return:
Id
Date
1
2022/01/01
1
2021/12/31
2
2021/12/20
2
2021/12/19
2
2021/12/18

var result = queryable
.GroupBy(entry => entry.Id)
.AsEnumerable()
.Select(entryGroup => entryGroup
.OrderByDescending(entry => entry.Date)
.Aggregate((EntryGroup: new List<Entry>(), GapDetected: false), (accumulated, current) =>
{
if (accumulated.GapDetected) return accumulated;
var previous = accumulated.EntryGroup.LastOrDefault();
if (previous == null || (previous.Date - current.Date).Days < 2) accumulated.EntryGroup.Add(current);
else accumulated.GapDetected = true;
return accumulated;
}))
.SelectMany(entryGroup => entryGroup.EntryGroup)
.ToList();
Note that only the GroupBy portion of the code is actually executed as an SQL query and the rest of the query is done locally since it can not be translated to SQL. I couldn't come up with a solution where the entire query could be translated to SQL but I wanted to show how this can be done with LinQ.

Return last 10 days data by date using Entity Framework

I want to return last 10 days list using Entity Framework by date. DateSigned is my date column. I already tried the code shown below, but this does not return the last 10 days of data, this returns 10 days back data. How can I fix it?
var Chart = dbcontext.CampaignEmails
.Where(x => x.DateSigned > DateTime.Now.AddDays(-10))
.ToList();

var tenDaysAgo = DateTime.Today.AddDays(-10);
var Chart = dbcontext.CampaignEmails.Where(x => x.DateSigned >= tenDaysAgo).ToList();
Is what you are looking for i guess.
If you only want 10 records you can use Take() LINQ method before the ToList() call.
Furthermore, you may need to order your results before even accessing them with a OrderBy().

RavenDB Select Distinct on a single property

I have an object stored in RavenDB with three properties: ID, Score, Date.
I want to create an index for retrieving the top 5 scores within a given date range. However, I only want to retrieve one record per ID. If a single ID shows up more than once in the top scores, I only want to retrieve the highest score for that ID, then move on to the next ID.
example scores:
Score____ID____
1000 1
950 1
900 1
850 2
800 2
750 3
700 4
650 5
600 6
550 7
desired query results:
Score____ID____
1000 1
850 2
750 3
700 4
650 5
I have created an explicit index similar to this (adjusted for simplicity):
Map = docs => from doc in docs
orderby doc.Score descending
select new
{
Score = doc.Score,
ID = doc.ID,
Date = doc.Date
};
I call my query with code similar to this (adjusted for simplicity):
HighScores = RavenSession.Query<Score, Scores_ByDate>()
.Customize(x => x.WaitForNonStaleResultsAsOfNow())
.Where(x => x.Date > StartDate)
.Where(x => x.Date < EndDate)
.OrderByDescending(x => x.Score)
.Take(5)
.ToList();
I don't know how to say "only give me the results from each ID one time in the list."

So a few pointers:
Don't order in the Map function. Maps are designed to just dump documents out.
Use the Reduce to do grouping, as this is the way they work by design
Add a hint to RavenDB that a particular column will be sorted in code, and what type of field it is.
By default, the map/reduce assumes the sorting is for text, even if it is a number - (I learned this the hard way and got help for it.)
So..
Just define the Map/Reduce index as normal, and add a sort condition at the end, like this:
public class Score_TopScoringIndex : AbstractIndexCreationTask<Score, Score>
{
public Score_TopScoringIndex()
{
Map = docs => from doc in docs
select new
{
Score = doc.Score,
ID = doc.ID,
Date = doc.Date
};
Reduce = results => from result in results
group result by result.ID into g
select new
{
Score = g.First().Score,
ID = g.Key,
Date = g.First().Date
};
Sort(x=>x.Score, SortOptions.Int);
}
}
Make sure the index is in the DB by using at the startup of your application:
IndexCreation.CreateIndexes(typeof(Score_TopScoringIndex).Assembly, documentStore);
Now, when you query, the OrderByDescending, it will be very fast.
using(var session = store.OpenSession())
{
var highScores = session.Query<Score>("Scores/TopScoringIndex")
.OrderByDescending(x=>x.Score)
.Take(5);
}

You can try using morelinq library
https://code.google.com/p/morelinq/
which has a DistintBy extension.

Converting SQL to LINQ needing to group records created per second

I am looking for a way in C# LINQ using lambda format to group records per second. in my search i have yet to find a good way to do this.
the SQL query is as follows.
select count(cct_id) as 'cnt'
,Year(cct_date_created)
,Month(cct_date_created)
,datepart(dd,cct_date_created)
,datepart(hh,cct_date_created)
,datepart(mi,cct_date_created)
,datepart(ss,cct_date_created)
from ams_transactions with (nolock)
where cct_date_created between dateadd(dd,-1,getdate()) and getdate()
group by
Year(cct_date_created)
,Month(cct_date_created)
,datepart(dd,cct_date_created)
,datepart(hh,cct_date_created)
,datepart(mi,cct_date_created)
,datepart(ss,cct_date_created)
now the closest i was able to come was the following but it is not giving me the right results.
var groupedResult = MyTable.Where(t => t.cct_date_created > start
&& t.t.cct_date_created < end)
.GroupBy(t => new { t.cct_date_created.Month,
t.cct_date_created.Day,
t.cct_date_created.Hour,
t.cct_date_created.Minute,
t.cct_date_created.Second })
.Select(group => new {
TPS = group.Key.Second
});
this appears to be grouping by seconds but not considering it as per individual minute in the date range and instead that second of every minute in the date range. To get Transactions per second i need it to consider each minute of the month, hour, day, minute separately.
The goal will be to pull a Max and Average then from this grouped list. Any help would be greatly appreciated :)

Currently you're selecting the second, rather than the count - why? (You're also using an anonymous type for no obvious reason - whenever you have a single property, consider just selecting that property instead of wrapping it in an anonymous type.)
So change your Select to:
.Select(group => new { Key = group.Key,
Transactions = group.Count() });
Or to have all of the key properties separately:
.Select(group => new { group.Month,
group.Day,
group.Hour,
group.Minute,
group.Second,
Transactions = group.Count() });
(As an aside, do you definitely not need the year part? It's in your SQL...)

C# LINQ Ignoring empty values in datatable

I have a datatable that I have grouped as follows:
var result = from data in view.AsEnumerable()
group data by new {Group = data.Field<string>("group_no")}
into grp
select new
{
Group = grp.Key.Group,
PRAS = grp.Average(c => Convert.ToDouble(c.Field<string>("pAKT Total")))
};
Now, the average function is also counting the empty cells in it's calculation. For example, there are 10 cells with only 5 populated with values. I want the average to be the sum of the 5 values divided by 5.
How can I ensure that it does what I want?
Thanks.

Maybe something like this:
PRAS = grp.Select(row => row.Field<string>("pAKT Total"))
.Where(s => !String.IsNullOrEmpty(s))
.Select(Convert.ToDouble)
.Average()

To my knowledge, that's not possible with the Average method.
You can however achieve the result you want to, with the following substitute:
PRAS = grp.Sum(c => Convert.ToDouble(c.Field<string>("pAKT Total"))) / grp.Count(c => !c.IsDBNull)
This only makes sense, when you want to select the "empty" rows in the group, but just don't want to include them in your average. If you don't need the "empty" rows at all, don't select them in the first place, i.e. add a where clause that excludes them.