Random Selection of Records

[oshlonger]

I have a basic report that lists out 13,200 Ids. There is no grouping or any other type of formating on these records. I would like to select a random sample of about 100 records.

I'm trying to create a formula that grabs every 132nd Id. I'm not sure if I'm going about this the correct way. Could someone please assist me?

 

[synapsevampire]

Create a formula to be used as a group that contains:

Rnd()

Sort the report by the formula and create a record selection formula on a group that has

recordnumber <= 100

-k

 

[lyanch]

Most databases have a random number generator. Using this assures better truely random selection without having to bring back all the records:

example:

Parameter ?PercenttoUse

enter this as a decimal ie 20% would be .2


SQL expression %Random:

Rand()

Selection formula

{?PercenttpUse} <= {%Random}


Lisa

 

[oshlonger]

Thanks. I did not know there was a Random function (Rnd). I was able to figure it out, not so easily but it worked. Here is how I did it:

I created a formula @counter and placed it in the details
[tt]WhilePrintingRecords;
NumberVar Counter := Counter +1;[/tt]

Then I created another formula @random and placed it in the details
[tt]{@counter} Mod 132[/tt]

Then I formatted my details section to suppress any record where @random <> 0

I know its a bunch more steps but I was happy to get where I was going.

Thanks for the help

 

[IdoMillet]

See faq767-3260 for a simpler approach.

Cheers,
- Ido CUT, Visual CUT, and DataLink Viewer:
view, e-mail, export, burst, distribute, and schedule Crystal Reports.

http://www.MilletSoftware.com

 

[lyanch]

That works well for a subset.. but probably not a truely random set. If you run the report twice, you will probably get the same records. You will need to incorporate either the SQL or crystal random to get a truely random sample.

Lisa