I would like to know if there is a more rapid way to multiply an array with a number in Visual Basic than the one presented below. I haven't found much on vectors in the help and seems that the only possible way would be to use the matrix class.
e.g. {1,3,4}*2 = {2,6,8}
I know this way to do that looping through the array:
Dim a() As Integer = {1, 2, 3, 4}
Dim b As Integer = 2
Dim c As Integer
For c = 0 To 3
a(c) = a(c) * b
Next
however the thing doesn't really work well for large arrays (in term of time), therefore I was wondering if the same operation can be performaed differently. For example using a vector in a way that with a single operation I can multiply all the values of an array at once.
Thanks
Scaling arrays
ke4vtw
hi,
i didn't understand your question but sounds you talk about the array bounds, to declare an array you have to know its length, if you don't know the length you can use ArrayList or Generics
i didn't use Generics b4 but ArrayList has ToArray method you can turn it to normal array search MSDN for it
hope this helps
hashi
Please read
http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=227937&SiteID=1
menardgi
My question is different- sorry if I wasn't clear enough.
I have added an example
Thanks
sasseen
hi,
i don't think this will take a long time i did that in an array has 10 million item and it took 400 millisecond
Dim array() As Integer = New Integer(10000000) {}
Dim i As Integer = 0
Do While (i < array.Length)
array(i) = i
i = (i + 1)
Loop
Dim n1 As DateTime = DateTime.Now
Dim i As Integer = 0
Do While (i < array.Length)
array(i) = (array(i) * 2)
i = (i + 1)
Loop
Dim n2 As DateTime = DateTime.Now
Dim s As TimeSpan = (n2 - n1)
Console.WriteLine(s.Milliseconds.ToString)
Dim i As Integer = 0
Do While (i < 20)
Console.WriteLine(array(i).ToString)
i = (i + 1)
Loop
but when i tried this with arraylist (its a collection like array but doesn't has bounds ) i created a class called it vector inherits from ArrayList class , and i added a method for multiply . it worked, but it took much more time
Namespace ConsoleApplication1
Class Program
Private Shared Sub Main(ByVal args() As String)
Dim array() As Integer = New Integer((1000000) - 1) {}
Dim i As Integer = 0
Do While (i < array.Length)
array(i) = i
i = (i + 1)
Loop
Dim itms As vector = New vector
itms.AddRange(array)
Dim n1 As DateTime = DateTime.Now
itms.Multiply(2)
Dim n2 As DateTime = DateTime.Now
Dim s As TimeSpan = (n2 - n1)
Console.WriteLine(s.Milliseconds.ToString)
Dim i As Integer = 0
Do While (i < 50)
Console.WriteLine(itms(i).ToString)
i = (i + 1)
Loop
End Sub
End Class
Class vector
Inherits ArrayList
Public Sub Multiply(ByVal by As Integer)
Dim i As Integer = 0
Do While (i _
< (Me.Count - 1))
Me(i) = (CType(Me(i),Integer) * 2)
i = (i + 1)
Loop
End Sub
End Class
End Namespace
hope this helps
Todd Virlee
Thanks very much for the extensive help
I have tried the first one and it seems to be working better
Cheers
Don Demsak XML MVP