Comments on: VBA Random Integers

By: Busybee

Busybee — Fri, 24 Jul 2009 06:05:00 +0000

@Tushar

I did go thru the page.. am just confused newbie…will it work as a worksheet function ?

I am just not sure which is one is right for me

Thx in advance.

By: Tushar Mehta

Tushar Mehta — Fri, 24 Jul 2009 05:45:00 +0000

Busybee:

See

Select elements at random without repetition
http://www.tushar-mehta.com/excel/newsgroups/rand_selection/

By: Busybee

Busybee — Fri, 24 Jul 2009 02:05:00 +0000

Hey,

Does this give unique random or there are repeats ??

I am looking @ creating a Quizz which pick unique random questions from different sections,however this below picks up repeats tooo

For j = 1 To SA
RD = WorksheetFunction.RandBetween(2, ACount)
Worksheets("Quiz Paper").Cells(j + 10, 1) = Worksheets("Section A").Cells(RD, 1)
Worksheets("Quiz Paper").Cells(j + 10, 2) = Worksheets("Section A").Cells(RD, 2)
Worksheets("Quiz Paper").Cells(j + 10, 3) = "Section A"
Worksheets("Quiz Paper").Cells(j + 10, 4) = Worksheets("Section A").Cells(RD, 3)
Next j

By: Tushar Mehta

Tushar Mehta — Thu, 23 Jul 2009 00:50:00 +0000

Dick wrote: "Because I'm using Round(), it will only pick the edges ~50% as often as the middle numbers. It seems that if I simply increase my range, that is reduce dLow by 0.5 and increase dHigh by .49, my distribution will be right. Technically it won't be right, but it will be close enough for government work. Whereas the old method wasn't even close enough for that."

So, why not just use INT in Excel or Int in VBA and get the correct result in the first place -- subject, of course, to the limitations in RAND (or Rnd). It's a lot easier than trying to fudge ROUND/Round. {grin}

By: Rob

Rob — Wed, 22 Jul 2009 13:39:00 +0000

they're all biased! use this: http://www.random.org/clients/http/

By: Doug Jenkins

Doug Jenkins — Wed, 22 Jul 2009 02:07:00 +0000

According to “Excel for Scientists and Engineers” (E. Joseph Billo) a new algorithm for random numbers was introduced in Excel 2003, because the old one wasn’t very good. Does anyone know if VBA uses the new algorithm or the old one (or something different)?

By: Jayson

Jayson — Tue, 21 Jul 2009 19:28:00 +0000

@JoshG

Thanks for the explanation. Good stuff to know.

By: JoshG

JoshG — Tue, 21 Jul 2009 19:08:00 +0000

Speed is one big advantage to writing your own. A few quick tests on my machine showed that my random function (like fzz's) is about 30-50 times faster than using the RandBetween Worksheetfunction. Also, previous to 2007 (at least in 2003), you needed to have the Analysis Tool Pak installed for RandBetween. Writing your own function helps improve compatibility.

-Josh

By: Jayson

Jayson — Tue, 21 Jul 2009 17:59:00 +0000

So, I’m really curious now. Why go through all the trouble of creating a random function when one exists? Is the built in function RANDBETWEEN biased? Are there advantages to building your own?

By: Jon Peltier

Jon Peltier — Tue, 21 Jul 2009 13:04:00 +0000

Dick -

fzz beat me to it, and Ross hinted at it first.

Your second procedure is essentially calculating Low + Int(High - Low + 0.99)

For an accountant, isn't that somewhat precise? I guess if you're an accountant for Enron, it's orders of magnitude too precise.