Re: [MS_AccessPros] randomly chosen groups

 

Russ-

Yes, that would be a surer way to ensure you get four equal groups.  On the first pass, I would assign numbers 1-4 and start with the "1" records and then pick "2" records until you get to ¼ of the total.  That way, you get enough records even if enough weren't assigned "1".

Do the UPDATE as Graham suggested and then do:

INSERT INTO Group1

(SELECT TOP nn FROM MyTable

ORDER BY [Group Number], [House Number]);

.. where nn is one-fourth of the total.

Then to do the DELETE:

DELETE * FROM MyTable

WHERE [House Number] IN

(SELECT [House Number] FROM [Group1]);

John Viescas, Author

Effective SQL

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http://www.viescas.com/ 

(Paris, France)

On Mar 3, 2017, at 1:57 PM, Russ dyspoz2@cox.net [MS_Access_Professionals] <MS_Access_Professionals@yahoogroups.com> wrote:

John and Graham,

Since this method will probably generate odd totals of households in the four groups would it be possible to do this a different way?  I slept on it and thought of this:  

Maybe put all the records in a temporary table, then pick a random 1/4 of the records and remove them to a tempgroup1 table, then take a random one third of the remaining households and move them to a tempgroup2 table, then take half of those remaining and remove them to a tempgroup3 table.  Then assign the group numbers as required and move them all back to the original table.  Is that possible?

Russ

On 3/2/2017 9:54 PM, graham@mandeno.com [MS_Access_Professionals] wrote:

Hi Russ

 

You don't actually need the Mod operation, because the Rnd() function returns a number between 0 and 0.99999999…  Thus, multiplying the result by 4 will give a number between 0 and 3.99999999…

 

You need to use the Int function to ensure this result is always rounded DOWN, and then finally add 1 if you want (1,2,3,4) instead of (0,1,2,3).

Thus, your UPDATE query  will look something like this:

UPDATE [Your Table Name] SET [Group Number]=Int(Rnd([House Number]) * 4) + 1;

Best regards,

Graham

---In MS_Access_Professionals@yahoogroups.com, <dyspoz2@...> wrote :

John,

Should I put this in the query field where I want the random number applied?  Such as in the Group Number field?  And I do want the groups to be numbered 1-4 so would the statement be modified like this?

Group:  (Rnd([Household Number]) * 4) Mod 5

Russ

You can use the Rnd function to do what you want in a query.

Group:  (Rnd([Household Number]) * 4) Mod 4

That will give you a random number between 0 and 3 to assign your groups.  Add 1 if you want groups 1 through 4.  Use that in an UPDATE query to assign the values.

NOTE:  You WILL get random numbers, but there's no guarantee that an equal number of households will be assigned to each group.

John Viescas, Author

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Posted by: John Viescas <johnv@msn.com>

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