Using Linq for Object Dataset Processing - vb.net

Question

I have a collection (IList(Of Sample)) of the following class:
Public Class Sample
Public sampleNum As String
Public volume As Integer
Public initial As Single
Public final As Single
End Class
This collection is filled from a regex that gets passed over a file.
What I want to do is use Linq to generate a collection of these for each unique samplenum using the following conditions.
For each samplenum:
Have the highest volume where the final is greater then one
If the sample has multiple records for this volume then pick the one with the the highest final
If the previous step leaves us with no records pick the record with the highest final ignoring volume
I am extremely new to Linq and just can't get my head around this. For now I have solved this using for each's and temporary lists but I am interested in how this would be handled using pure Linq.
Sample Data:
samplenum | volume | initial | final
1 | 50 | 8.47 | 6.87
1 | 300 | 8.93 | 3.15
2 | 5 | 8.28 | 6.48
2 | 10 | 8.18 | 5.63
2 | 5 | 8.33 | 6.63
2 | 10 | 8.26 | 5.58
3 | 1 | 8.31 | 0.75
3 | 5 | 8.19 | 0.03
4 | 50 | 8.28 | 6.55
4 | 300 | 7.19 | 0.03

Answer 1

This should hopefully solve your problems:
Dim source As IEnumerable(Of Sample)
' Get the data...
Dim processed = source _
.GroupBy(Function(s) s.sampleNum) _
.Select(Function(s) Process(s))
Dim array = processed.ToArray()
Console.ReadLine()
The Process function:
Private Function Process(ByVal sequence As IEnumerable(Of Sample)) As Sample
Dim filtered = (
From s In sequence
Where s.final > 1
Order By
s.volume Descending,
s.final Descending
)
' If we don't have any elements after the filtering,
' return the one with the highest final.
' Otherwise, return the first element.
If Not filtered.Any() Then
Return (From s In sequence Order By s.final Descending).FirstOrDefault()
Else
Return filtered.First()
End If
End Function

Answer 2

Try this. I haven't tried it but it should do what you want. There is probs a better way of doing this:
' For each sample number in the list
For Each el In (From p In lst Select p.sampleNum).Distinct()
' can cause odd results in some cases so always put the foreach var into another var
Dim var As String = el
' get another "list" but for this sample num
Dim res As IEnumerable(Of Sample) = lst.Where(Function(p) p.volume > 1 AndAlso p.sampleNum = var)
Dim sam As Sample ' the result
If Not res Is Nothing And res.Any() Then
' we have a result, so get the first result where the
sam = res.Where(Function(p) p.volume = res.Max(Function(x) x.volume)).First()
Else
' we have no results, so resort back to the normal list, for this sample number
sam = lst.Where(Function(p) p.sampleNum = var AndAlso p.volume = lst.Max(Function(x) x.volume)).First()
End If
'
' do what ever with the sample here
'
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