How to list of (list of integer)) to string with string.join method?

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I have List3 as List(Of List(Of Integer))

Dim List3 As New List(Of List(Of Integer))
Dim List1 As List(Of Integer) = {1, 2, 5, 7}.ToList
Dim List2 As List(Of Integer) = {5, 3, 2, 1}.ToList
List3.Add(List1)
List3.Add(List2)

How can i get string like this

1,2,5,7 
5,3,2,1

What I have tried:

Dim str As String = String.Join(vbNewLine, List3)

Posted 5-Oct-19 8:12am

gacar

Updated 8-Oct-19 8:24am

v2

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2 solutions

Solution 1

You have to iterate the collection and format the output:

VB

Imports System.Collections.Generic
Imports System.Linq
Imports System.Text

Public Shared Function DumpListOfList(Of T)(List(Of List(Of T)) list) As String
   Dim builder As New StringBuilder()
   For Each sublist As List(Of T) In list
      builder.AppendLine(String.Join(",", sublist.ToArray()))
   Next
   builder.Remove(builder.Length - 2, 2) '' Get rid of the last CrLf
   Return builder.ToString()
End

'' Usage:
Dim result As String = DumpListOfList(List3)

Posted 5-Oct-19 8:25am

phil.o

Updated 5-Oct-19 8:30am

v3

Comments

Maciej Los 8-Oct-19 16:06pm

5ed!

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Richard Deeming · Accepted Answer · 2019-10-08T08:25:00

Solution 3

A simpler solution using LINQ:

VB.NET

Dim str As String = String.Join(vbNewLine, List3.Select(Function (list) String.Join(",", list)))

Lambda Expressions (Visual Basic) | Microsoft Docs[^]

Posted 8-Oct-19 8:25am

Richard Deeming

Comments

Maciej Los 8-Oct-19 16:06pm

5ed!

phil.o 8-Oct-19 17:42pm

5'd also.
There's so much time I left VB now, generics did not exist yet; when I have to write some code block in VB, I think about it in c#, and have to go through a mental translation process. Let alone Linq... Thanks Richard.

Richard Deeming 9-Oct-19 6:48am

Same here - I haven't done any serious VB.NET work for over 15 years. :)

gacar 10-Oct-19 7:24am

This is! Thank you very much.