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for each where

Posted on 2010-09-03
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Last Modified: 2012-05-10
Is there a way in vb.net select all elements from a for each statement using a where?
I am not a fan of linq for speed purposes.
It is for a game type program so speed is critical.


I want to iterate through only some  elements of a list . Those elements meet some condition.
Like  iterate through a list of objects where some property is set to false.

I can use a for each and and if statement currently but I am after a better way.


  For Each pt In Mpl
            If pt.direction = missileType Then
...
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Question by:jagguy
7 Comments
 
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by:Wayne Taylor (webtubbs)
ID: 33601628
The only way to do that is with LINQ.    Dim pts = From pt In Mpl Where pt.Direction = missleType    For Each pt In pts        ''''    NextWayne
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Expert Comment

by:Mike Tomlinson
ID: 33601700
You can use the List.FindAll() method:
http://msdn.microsoft.com/en-us/library/fh1w7y8z.aspx

Really not sure if it is "better" though...just different...

Made up example:
Public Class Form1



    Private Const missileType As Integer = 0



    Private Class Something

        Public direction As Integer

    End Class



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim Mpl As New List(Of Something)



        ' ...



        For Each pt In Mpl.FindAll(AddressOf FindMissiles)

            ' ...

        Next

    End Sub



    Private Function FindMissiles(ByVal pt As Something) As Boolean

        Return pt.direction = missileType

        ' ... obviously a more complicted match algorithm could be used in here! ...

    End Function



End Class

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Expert Comment

by:HainKurt
ID: 33601754
what about creating a dynamic datatable, put elements into it (maybe you already getting values from db, in this case you may have a datatable already)
then you can use rowfilter property of datatable.defaultview.rowfilter="id > 10 and id < 20"

--> http://msdn.microsoft.com/en-us/library/system.data.dataview.rowfilter.aspx
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Author Comment

by:jagguy
ID: 33601903
thanks for the replies.

actually it looks worse with all these  extra functions and I am wooried about speed as well, database no way and MSDN examples dont always clarify things. Who wites MSDN stuff and does it get proof read for simplicity?
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by:Gururaj Badam
ID: 33602163
I'm a C# guy, pardon my syntax.

For Each pt In Mpl.Where pt => pt.direction = missileType


this will only iterate elements matching your where condition. I don't know why you feel LINQ will slow down your processing when it's actually design gain performance.
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Author Comment

by:jagguy
ID: 33605978
i havent read anywhere Liunq speeds up performance and have only heard it slows things down because of its design.

Could you show me any article where it says iterating through a list of data using linq is quicker ( or no slwere)than using an if condition .
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Gururaj Badam earned 500 total points
ID: 33606127
@jagguy - I couldn't believe until i did a test. You're right.
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