Coding Question

Hi all,

I just started to learn gh VB.net. I cannot run thorough a easy code because of some bug in it.

I got a group of lines with different length as input, just wanna put lines with the length that bigger than some number into another arraylist as output.

if anyone of you has an idea to debug, really appreciate your comment and suggestion. Many thanks!

Below is the code:

Private Sub RunScript(ByVal y As List(Of Line), ByVal x As Double, ByRef A As Object)

    Dim Input_Line As New Line
    Dim New_Line As New Line
    Dim New_Lines As List( Of Line )
    Dim i As Integer

For i = 0 To y.Count()

Input_Line = y(i)

      If Input_Line.Length < x Then
        New_Line = Input_Line
      End If
      New_Lines.Add(New_Line)
    Next

A = New_Lines

End Sub

Replies to This Discussion

Permalink Reply by David Rutten on June 22, 2011 at 7:53am

For i = 0 To y.Count()

This is the problem. If the list contains 10 lines, then this loop will run from zero to ten:

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

which -if you count it- is actually eleven times. Your loop should go to y.Count - 1. Or, you could use a For...Each loop, circumventing the problem altogether:

Dim shortLines As New List(Of Line)

For Each segment As Line in y

If (segment.Length < x) Then

shortLines.Add(segment)

End If

Next

A = shortLines

--------------------------------

Another problem is this line of code:

New_Lines.Add(New_Line)

It is located inside the loop but outside the If statement, meaning it gets run every single iteration. This fills up the short line list with duplicates.

-------------------------------

Here's something else which is redundant:

Dim Input_Line As New Line

Apart from the fact that you don't need a special variable for this at all, you also don't need to add a New keyword. The type Line in RhinoCommon (just like Point3d, Vector3d, Plane, BoundingBox etc. etc.) are Structures, not Classes. Structures always exist when they are defined, whereas Classes can be null ("Nothing" in VB).

-------------------------------

Some more advice:

Dim i As Integer

For i = 0 To y.Count()

You can merge these two lines into one. VB.NET allows you to declare your iteration variable inside the loop:

For i As Integer = 0 To y.Count - 1

--------------------------------

If you don't like the For...Each approach at the top of this answer, here's how to write this using a For...To loop:

Dim shortLines As New List(Of Line)

For i As Integer = 0 To y.Count - 1

If (y(i).Length < x) Then

shortLines.Add(y(i))

End If

Next

A = shortLines

ps. A personal preference of mine is that I always encase the expressions inside If...Then statements in brackets. You technically don't need to do this, but I find it makes the code more readable.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by waya on June 22, 2011 at 8:07pm

Such a professional reply!~ Thanks very much! !

Actually, i did a lot monkey rvb before, and now I am struggling with the transition from monkey's vb to grasshopper's vb as a study. It seems a long way to go for me~~, even though I know the basic logic... Hopefully it would be better when I get more familiar with syntax and data transfer in grasshopper vb.net.

Anyway, thanks again!

Permalink Reply by Steve Lewis on June 22, 2011 at 11:16pm

When coding check the origin used when referencing elements in an array or list.

VBA uses an origin index of 1 for indexing elements. Most modern code like VB.Net always use an index of 0 to reference the first element.

Typically the last element of a collection or array will always by referenced as
The total number of elements (count) -1 and first is 0.

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