topic How is Rand calculated how is it seeded? in QlikView

How is Rand calculated how is it seeded?

dgreenberg — Mon, 28 Mar 2016 16:50:27 GMT

I am working on a sampling routine.

Our statistician wants to know if we can adjust the seed - his words not mine.

His expectation is if I re-load the data in the same order and pick a random row using the same seed then it would yield the same results.

I am not sure that's going to work but figured I would post in the community to see what everyone has to say.

Thanks

Dan

Re: How is Rand calculated how is it seeded?

sunny_talwar — Mon, 28 Mar 2016 16:55:36 GMT

I have never done it, but tried looking it up on Google and QV's help. From the looks of it, it doesn't seem it is possible, unless there is a work around available.

Re: How is Rand calculated how is it seeded?

Anonymous — Mon, 28 Mar 2016 17:15:55 GMT

You can test with the QlikView Test Script and you'll see that with every reload it generates independent random values.

So the answers for your statistician are :

No: You cannot adjust the seed

No: It will not yield the same results when reloaded again

I ain't got clue how rand() actually works under the bonnet though.

***************************************************

Characters:

Load Chr(RecNo()+Ord('A')-1) as Alpha, RecNo() as Num autogenerate 26;

ASCII:

Load

if(RecNo()>=65 and RecNo()<=90,RecNo()-64) as Num,

Chr(RecNo()) as AsciiAlpha,

RecNo() as AsciiNum

autogenerate 255

Where (RecNo()>=32 and RecNo()<=126) or RecNo()>=160 ;

Transactions:

Load

TransLineID,

TransID,

mod(TransID,26)+1 as Num,

Pick(Ceil(3*Rand1),'A','B','C') as Dim1,

Pick(Ceil(6*Rand1),'a','b','c','d','e','f') as Dim2,

Pick(Ceil(3*Rand()),'X','Y','Z') as Dim3,

Round(1000*Rand()*Rand()*Rand1) as Expression1,

Round( 10*Rand()*Rand()*Rand1) as Expression2,

Round(Rand()*Rand1,0.00001) as Expression3;

Load

Rand() as Rand1,

IterNo() as TransLineID,

RecNo() as TransID

Autogenerate 1000

While Rand()<=0.5 or IterNo()=1;

Re: How is Rand calculated how is it seeded?

dgreenberg — Mon, 28 Mar 2016 17:17:25 GMT

Thanks.

That is what I expected just needed some backup to explain to the statistician that we can't do that.

Re: How is Rand calculated how is it seeded?

swuehl — Mon, 28 Mar 2016 17:24:42 GMT

Well, if you need the same sequence of "random" numbers on every reload, you could probably either

a) use a small VBScript calling RND / Randomize

b) create a set of numbers using QV script Rand() function, write this to a QVD and use this file