How to select only not null objects from list

Question

I have a list of objects of type Pump, each one of them holding a reference to an object of type Valve, exposed through its property Valve.

Public Class Pump

    Private _valve As Valve 'may be Nothing

    Public ReadOnly Property Valve() As Valve
        Get
            Return _valve 
        End Get
    End Property
End Class

However, the valve can exist or just be Nothing.

It there an easy way to select all the valves and put them in a list?

I tried this:

_pumps.Select(Of Valve)(Function(p As Pump) p.Valve).ToList

But I get a list with some of the objects being Nothing, since there was no valve asigned to the correspondent pump.

I have finally done this:

Dim valves As New List(Of Valve)
    For Each p As PumpIn _pumps
        If p.Valve IsNot Nothing Then
            valves.Add(p.Valve)
        End If
    Next

But I was wondering if there is a more compact way of doing it:

Thanks!

Giannis Paraskevopoulos · Accepted Answer · 2014-08-29 18:41:28Z

3

I think the following will help:

_pumps.Where(Function(p) p.Valve IsNot Nothing).Select(Of Valve)(Function(p As Pump) p.Valve).ToList

edited Aug 29, 2014 at 18:41

answered Aug 29, 2014 at 12:20

Giannis Paraskevopoulos

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4 Comments

Meta-Knight Over a year ago

The Where clause should check for null valve not null pump.

Giannis Paraskevopoulos Over a year ago

@meta-knight You were right and i changed it, though i think a downvote was a bit too harsh in this case. ;-)

Meta-Knight Over a year ago

Yeah, you were on the right track and now it's fixed. Upvoted instead :-) One more thing to note, you can just write .Select(Function(p) p.Valve) without the (Of Valve) and As Pump parts which are superfluous.

Giannis Paraskevopoulos Over a year ago

@meta-knight I know and this is how i would write it, but i wanted to keep the changes to the minimum.

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