Re: Random With Odds

** Reply to note from richard@zend.com (Richard Lynch) Mon, 03 Jul 2000 22:03:42 -0500 > I am about to create a BIG script that will allow a banner to rotate.. I > want to allow the user to select a weight for each banner.. 1 showing up > 1.5x as much as 2, 2 showing up 1.5x more than 3, 3 showing up 1.5x more > than 4, etc... how would I do that?? is there a way to setup rand to take in > account the odds of picking one number, and is it possible to change those > odds?? > so 4 = 1 # 1 for the base 3 = 1.5 # 1 * 1.5 2 = 2.25 # 1.5 * 1.5 1 = 3.375 # 2.25 * 1.5 Multiply by 8 to eliminate fractions 4 = 1 * 8 = 8 3 = 1.5 * 8 = 12 2 = 2.25 * 8 = 18 1 = 3.375 * 8 = 27 ------ Add them together 65 So you have 65 possibilities, 8 of them result in 4, 12 result in 3, 18 result in 2 and 27 result in 1. If you have an evenly distributed random number it is easy to say: 0- 7 = 4 8-19 = 3 20-37 = 2 38-65 = 1 IF those are the only choices, and the frequencies, all the above can be done by hand. You end up with an array like $Ods = array( 4,4,4,4,4,4,4,4, # 8 fours 3,3,3,3,3,3,3,3,3,3,3,3, # 12 threes 2,2,2,2,2,2,2,2,2, 2,2,2,2,2,2,2,2,2, # 18 twos 1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1 ); # 27 ones Now all you have to do: $Result = $Ods[ rand( 0, 65 ) ]; By definition the result of the random value should be evenly distributed, so the array above should be valid. Most people looking at it would think it fixed, and would be happer seeing an array like: array( 1,1,1,2,2,3,4,1,1,1,2,2,3,4,1,1,1,2,2,3,4,3, 1,1,1,2,2,3,4,1,1,1,2,2,3,4,1,1,1,2,2,3,4,3, 1,1,1,2,2,3,4,1,1,1,2,2,3,4,1,1,1,2,2,3,3 ); But realy mixing them up does nothing to change the ods. Since you are writing a big script to do the job, you probably want a variable number of entries, and a varialble hit probablility. That means you need to script all of this. Hint: Don't allow fractions in your frequencies. You can't have half an array entry, so if you have fractions you have to multiply all the items to eliminate the fractional part. If you can eliminate the fractions up front you can do much easier. If you numbers were 2 instead of 1.5 it would be 4 = 1 # number hits on 4 (1) 3 = 2 # Hits on 4 * 2 2 = 4 # Hits on 3 * 2 1 = 8 # Hits on 2 * 2 The ods array could be array( 1,1,1,1,1,1,1,1,2,2,2,2,3,3,4 ); Or you could calculate the breakpoints as 1 = 0 - 7 # 8 entries or 0 - thru the number of hits on 1 2 = 8 - 11 # 4 entries or Last end + 1 thru last end + hits on 2 3 = 12 - 13 # 2 entries or last end + 1 thru last end + hits on 3 4 = 14 # 1 entry or last end + 1 thru nothing, since there is only 1 Clear as mud, I presume... Rick Widmer Internet Marketing Specialists www.developersdesk.com