Question

After two years of C#, my VB.NET is a bit rusty. I have two Lists. Let’s call them originalList and targetList. Here is my C# code:

for(int i = 0; i<originalList.Count; i++) {     bool isMatch = false;     foreach (string t in targetList)     {         if(String.Compare(originalList[i], t, true) == 0)         {             isMatch = true;             break;         }     }     if(isMatch)     {         originalList.RemoveAt(i);         i--;     } } 

And my VB.NET code is this:

Dim i as Integer For i = 0 To originalList.Count - 1     Dim isMatch as boolean = false     For Each t As String In targetList         If String.compare(originalList(i), t, true) = 0 Then             isMatch = true             Exit For         End If     Next      If isMatch Then         originalList.RemoveAt(i)         i -= 1     End If Next 

But I got an index-out-of-range error with my VB.NET code. Where did I get it wrong?

Answer 1

Consider this – it’s a far more elegant way of achieving what you’re trying to do – and that is removing items from your original list that appear in your target list. Consider the following lists:

Dim OriginalList As New List(Of String)(New String() {'a', 'b', 'c', 'd'}) Dim TargetList As New List(Of String)(New String() {'a', 'b', 'c'}) 

And here’s how I’d remove all the items from the original that appear in the target…

OriginalList.RemoveAll(Function(OriginalItem) TargetList.Contains(OriginalItem)) 

Which in C# would be written:

OriginalList.RemoveAll(OriginalItem => TargetList.Contains(OriginalItem)); 

The less code you use to achieve a task, the less chance that coding bugs could be introduced.

Side Note: This is very similar to an algorithm to test subsets. If you want to find out if set A is a subset of B, then you can iterate through B removing any corresponding items from A. Once you’ve finished iterating through B, if there are any items left in A, then it wasn’t a subset of B. If there are no items left, then it was a subset of B.