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Probabilty Formula

Discussion in 'PHP' started by gigamike, Jun 6, 2008.

gigamike Active Member

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#1

Guys,

Any suggestion for probability logic. Example

Ads=weight
Ads1=100%
Ads2=200%
Ads3=100%

Then when i select random, there is a big chances for ads2 to be selected since it has 200%

I got an idea but im thinking its not the best way

I create an array based on the %

$choices=array('Ads1', 'Ads2', 'Ads2', 'Ads3');
$selected=array_rand($choices) ;

Any other idea?

Thanks,

Mike

gigamike, Jun 6, 2008 IP
GLD Well-Known Member

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#2
You could try this:

Here's an algorithm to make a weighted selection of an item from an array.
Say we have an array $items with keys as items and values as corresponding weights.
For example:

<?php $items = array( item1 => 3, item2 => 4, item3 => 5, ); ?>

PHP:

i.e. we want to choose item1 25% of the time, item2 33.3% of the time and item3 41.6% of the time.
Here's a function that works when the weights are positive integers:

<?php function array_rand_weighted($values) { $r = mt_rand(1, array_sum($values)); foreach ($values as $item => $weight) { if ($r <= $weight) return $item; $r -= $weight; } } ?>

PHP:

Enjoy!
Click to expand...
GLD, Jun 6, 2008 IP

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