Find gap in datetime range with Linq to sql in vb.net - vb.net

Question

I would like use linq to sql to query (prefer vb.net but c# example will do a table for records that are grouped by a field in the table and have holes in the datetime field that are greater than 30 minutes. My table has records added at regular intervals during the lifetime of a job generally every two minutes occasionally there is a period of missing records. The table holds records for multiple jobs in the same date range although I have only added one with a different job number to highlight this. The table looks like the table below.

Answer 1

Edit:
VB .NET, untested:
Dim jobs = New List(Of Job)() From {
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 0, 0, 0),
.JobGroup = 1,
.Value = 100
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 2, 0, 0),
.JobGroup = 1,
.Value = 200
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 4, 0, 0),
.JobGroup = 1,
.Value = 300
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 7, 0, 0),
.JobGroup = 2,
.Value = 600
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 40, 0, 0),
.JobGroup = 1,
.Value = 400
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 42, 0, 0),
.JobGroup = 1,
.Value = 500
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 9, 0, 0),
.JobGroup = 2,
.Value = 700
},
New Job() With {
.Date = New DateTime(2020, 10, 1, 1, 49, 0, 0),
.JobGroup = 2,
.Value = 800
}
}
Dim gaps = jobs.OrderBy(Function(x) x.JobGroup).Skip(1).Zip(jobs, Function(c, p) New With {Key
.Current = c, Key
.Previous = p, Key
.Gap = (c.Date - p.Date).TotalMinutes
}).Where(Function(x) x.Gap >= 30 AndAlso (x.Current.JobGroup = x.Previous.JobGroup))
For Each gap In gaps
Console.WriteLine($"Job Group: {gap.Current.JobGroup}, Gap (minutes): {gap.Gap}, Value: {gap.Current.Value} ")
Next
End Sub
Class Job
Public Property JobGroup As Integer
Public Property Date As DateTime
Public Property Value As Integer
End Class
I´m a bit rusty at VB so I´ll give you an C# answer like you said.
//Sample Data //Year, Month, Day, Hour, Minute, Second, Millisecond
var jobs = new List<Job>() { new Job() { Date = new DateTime(2020, 10, 1, 1, 0, 0, 0), JobGroup = 1 ,Value = 100},
new Job() { Date = new DateTime(2020, 10, 1, 1, 2, 0, 0),JobGroup = 1 ,Value = 200} ,
new Job() { Date = new DateTime(2020, 10, 1, 1, 4, 0, 0),JobGroup = 1 ,Value = 300},
new Job() { Date = new DateTime(2020, 10, 1, 1, 7, 0, 0), JobGroup = 2 ,Value = 600},
new Job() { Date = new DateTime(2020, 10, 1, 1, 40, 0, 0),JobGroup = 1 ,Value = 400},
new Job() { Date = new DateTime(2020, 10, 1, 1, 42, 0, 0), JobGroup = 1 ,Value = 500},
new Job() { Date = new DateTime(2020, 10, 1, 1, 9, 0, 0), JobGroup = 2 ,Value = 700},
new Job() { Date = new DateTime(2020, 10, 1, 1, 49, 0, 0), JobGroup = 2 ,Value = 800}
};
//Determine gaps
var gaps = jobs.OrderBy(x => x.JobGroup) //don´t mix job group IDs
.Skip(1) //To compare current and previous job record
.Zip(jobs, (c, p) => new { Current = c, Previous = p, Gap = (c.Date - p.Date).TotalMinutes }) //Determine gap between current and previous record
.Where(x => x.Gap >= 30 && (x.Current.JobGroup == x.Previous.JobGroup)); //Only take those gaps which are GT 30 minutes
foreach(var gap in gaps)
{
Console.WriteLine($"Job Group: {gap.Current.JobGroup}, Gap (minutes): {gap.Gap}, Value: {gap.Current.Value} ");
}
//Result:
//Job Group: 1, Gap(minutes): 36, Value: 400
//Job Group: 2, Gap(minutes): 40, Value: 800
My sample data is just a simple DTO
class Job
{
public int JobGroup { get; set; }
public DateTime Date { get; set; }
public int Value { get; set; }
}

Answer 2

Be aware that #Alex B's solution requires the table be pulled into memory before executing because .Zip isn't translatable to SQL. in this case, you may want to look into doing this via a view leveraging SQL's Lag...Over syntax and just consume the results of that via a Linq to SQL Entity. Something like:
CREATE VIEW vwJobGaps AS
SELECT Job, DateAdded, PrevDateAdded, Value,
DATEDIFF(m, PrevDateAdded, DateAdded) As MinutesFromLastJob
FROM
(SELECT Job, DateAdded, Value,
LAG(DateAdded, 1, null) over (Partition by Job order by DateAdded ASC) As PrevDateAdded
FROM MYTable))
And then for your entity:
<Table("vwJobGaps")>
Public Class JobGap
Public Property Job As Integer
Public Property DateAdded As DateTime
Public Property PrevDateAdded As DateTime
Public Property Value As Decimal
Public Property MinutesFromLastJob As Integer
End Class
Since you're using a view here, you can add additional filters, joins, etc using standard LINQ to SQL just as you would other tables:
var query = from gap in dc.JobGaps
where gap.MinutesFromLastJob > 30
'' select clause not needed in vb