boilerplate-service-probability.md

Probability Service

Useful for A/B Testing, User Segmenting, Weighted Strategies etc...

Live Example: https://implode.io/av1Cy9

Random Weighted Prediction

Guess a random result using weight to favor a specific distribution of predicatable outcomes.

$color = RandomWeighted::prediction([
  'orange' => 2.5, // ~25% chance
  'green' => 3.5, // ~35% chance
  'red' => 4.0, // ~40% chance
]);

Practical Example:

Ads with higher prices will be shown more often then ads with lower prices:

$slug = RandomWeighted::prediction([
  'politics' => 250, 
  'sports' => 240,
  'tech' => 190,
]);

Advertisement::category($slug)->inRandomOrder()->first();

Simulation: Totals over x rounds.

$results = RandomWeighted::simulation(100, [
  "a" => 2, 
  "b" => 3,
  "c" => 1,
]);

// Totals over 100 rounds.
[
  "a" => ?, 
  "b" => ?,
  "c" => ?,
]

Service Class

<?php declare(strict_types=1);

namespace App\Services\Probability;

use Illuminate\Support\Collection;

class RandomWeighted
{
     /**
     * Random Weighted Key
     * @param array $weights
     * @return string|null
     * @source
     */
    public static function prediction(array $weights): ?string
    {
        $sum = 0;
        $weights = Collection::make($weights)->sort();
        $random = mt_rand(1, $weights->sum());
        foreach($weights as $key => $weight){
             if (($sum += $weight) >= $random) {
                return $key;
            }
        }
        return null;
    }

    /**
     * Sum Rounds of Random Weights
     * @param array $weights
     * @param int $rounds
     * @return Collection
     */
    public static function simulation(int $rounds, array $weights): Collection
    {
        $results = Collection::times($rounds, function() use ($rounds, $weights){ 
            usleep(mt_rand(0, $rounds));
            return static::prediction($weights);
        });
        return Collection::make($weights)->map(function ($weight, $key) use ($results) {
            return $results->filter(function($result) use ($key){
                return $result === $key;
            })->count();
        });
    }
}