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Resolved Has Anyone Tested Rand() on 2017R3

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  1. Glenn Barber
    Glenn Barber
  2. PowerBuilder
  3. Wednesday, 12 September 2018 23:42 PM UTC

We have an application which needs to select a random row from about 15000 rows.  

we are getting the value from

ll_row = Rand(ll_rowcount)

During repeated testing Ive noticed a unexpected high frequency of specific numbers (like 993) which defy the usual odds.

I am curious if anyone else has worked extensively with Rand in PB2017R3 and had similar experiences(or the contrary)

Best

Glenn Barber

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Responses (4)
Glenn Barber
Glenn Barber Accepted Answer Pending Moderation
  1. Saturday, 15 September 2018 22:50 PM UTC
  2. PowerBuilder
  3. # 1

We are using the Randomize (0) methods before calling Rand(n).  However we notice that the routine seems to be unreliable when n is larger than 14K.  I am researching what value of n causes it not to provide sufficiently random values.

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Glenn Barber
Glenn Barber Accepted Answer Pending Moderation
  1. Saturday, 15 September 2018 22:38 PM UTC
  2. PowerBuilder
  3. # 2

We are running the windows version - java is not a workable solution for us.

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Olan Knight
Olan Knight Accepted Answer Pending Moderation
  1. Friday, 14 September 2018 14:47 PM UTC
  2. PowerBuilder
  3. # 3

One alternative is to run a Java program to get your random number. Since PB does not support callbacks, your Java code will need to set the result in a manner that your PB code can find; i.e. a text file.
https://dzone.com/articles/random-number-generation-in-java

You can also create a function in C that does this:
https://www.geeksforgeeks.org/generating-random-number-range-c

 

Olan

 

 

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Glenn Barber
  1. Glenn Barber
  2. Saturday, 15 September 2018 22:47 PM UTC
Give the similarity of the methods - I would bet that the powerbuilder version is using the C++ method described.



That said, It appears that the PowerBuilder Rand(n) method misbehaves for long's around 14K or higher.
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Chris Pollach @Appeon
Chris Pollach @Appeon Accepted Answer Pending Moderation
  1. Thursday, 13 September 2018 13:55 PM UTC
  2. PowerBuilder
  3. # 4

Hi Glenn;

   Have you tried the Randomize ( ) command before using the Rand ( ) method to reset the "seed" number generator?

For example:

Randomize (ll_rowcount)

ll_row = Rand(ll_rowcount)

 

HTH

Regards ... Chris

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Markus Eckert
  1. Markus Eckert
  2. Thursday, 13 September 2018 14:02 PM UTC
Or just Randomize(0)

If ll_rowcount is the same between two runs, the Random number sequence will be the same.
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Glenn Barber
  1. Glenn Barber
  2. Saturday, 15 September 2018 22:43 PM UTC
I dont understand this response - are you telling me that if I Set Randomize(0) and then run

ll_row = Rand(ll_rowcount) successively that I will get the name number?? Or are you saying that if I run Rand(ll_rowcount) repeatedly in two different programs that the sequence each program returns on successive calls will be the same if ll_rowcunt is the same?



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Chris Pollach @Appeon
  1. Chris Pollach @Appeon
  2. Saturday, 15 September 2018 23:37 PM UTC
Hi Glenn;

The Radomize command resets the internal counters. You could use this command instead of Rand() or execute it every once in a while to reset the internal mechanisms before using Rand().

Regards ... Chris
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