Vb, sorting lists

Question

I have a question concerning sorting lists of classes in VB.Net. It seems every subject which is discussing this kind of sorting is not really clear for me.

I have a class Language with the following variables: - Lang as a string - Knowledge as a integer

I have got a list containing a couple of language classes in it. How can I sort on the Lang variable (Alphabetically sort the language classes in the list)?

Greetings,

Victor Zakharov · Accepted Answer · 2014-06-24 13:29:59Z

2

Implement IComparable on your class, then use Sort:

Private Class Language : Implements IComparable(Of Language)
  Public Property Lang As String
  Public Property Knowledge As Integer

  Sub New(lang As String)
    Me.Lang = lang
  End Sub

  Public Function CompareTo(other As Language) As Integer _
                                    Implements IComparable(Of Language).CompareTo
    Dim comp As Integer = Me.Lang.CompareTo(other.Lang)
    'If comp = 0 Then Return Me.Knowledge.CompareTo(other.Knowledge)
    Return comp
  End Function
End Class

Sub Main()
  Dim lst As New List(Of Language)
  lst.Add(New Language("fr"))
  lst.Add(New Language("en"))
  lst.Add(New Language("de"))
  lst.Sort()
End Sub

EDIT: Added a hint on how to sort by multiple properties.

edited Jun 24, 2014 at 13:29

answered Jun 23, 2014 at 13:33

Victor Zakharov

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5 Comments

Revils Over a year ago

Thank you very much, that was all info I needed!

Revils Over a year ago

Is it also possible to sort/compare on two variables? Say I first sort on Lang first. if I have two Lang, than sort on the knowledge level?

Victor Zakharov Over a year ago

@Sliver2009: You can put an if statement, i.e. If result of CompareTo equals to 0, make another CompareTo, and return that.

Victor Zakharov Over a year ago

@Sliver2009: I modified my example, please check it out. Reference: CompareTo @ MSDN

Revils Over a year ago

Thanks, I am not an expert in VB.Net, but I get the rationale behind comparing now!

Community · Accepted Answer · 2017-05-23 12:05:43Z

2

This was answered in a previous StackOverflow question: Sort a List of Object in VB.NET

Use Sort along with a custom function to compare the Lang variable.

theList.Sort(Function(x, y) x.Lang.CompareTo(y.Lang))

edited May 23, 2017 at 12:05

CommunityBot

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answered Jun 23, 2014 at 13:18

James Hunt

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5 Comments

Revils Over a year ago

I saw that topic to, but I do not get the following: Function(x, y) x.Lang.CompareTo(y.Lang)

Grim Over a year ago

Which version of the .NET Framework are you using? Older versions do not support these functions; you need LINQ and lambda functionality to do it.

James Hunt Over a year ago

Sort accepts a function as an argument. This function is how two elements are compared to decide how one element is put infront of another. The function written in that code compares the 2 elements by their Lang variable, ordering them via it.

Revils Over a year ago

So something like: Private Sub Counter(Language x, Language y) if x > y then ..? End Sub list.Sort(Counter xLang.CompareTo(y.Lang) And I do not understand how a function should be? (It should return two values? Both x and y?)

James Hunt Over a year ago

Grim, even with .NET 2.0 you can specify a function as an argument for Sort, you just need it predefined.

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