WP_Model-filter.php

<?php 
Class City extends WP_Model{
    public $postType = 'city';

    public $attributes = [
        'population',
    ];
  
    public $filter = [
        'population'
    ];
  
    public function _filterPopulation($value){
        $suffixes = ['', 'K', 'M', 'G', 'T'];
        $suffixIndex = 0;

        while(abs($value) >= 1000 && $suffixIndex < sizeof($suffixes)){
            $suffixIndex++;
            $value /= 1000;
        }

        return ( $value > 0
            ? floor($value * 1000) / 1000
            : ceil($value * 1000) / 1000
        ) . $suffixes[$suffixIndex];
    }
}
  
$london = City::insert([
    'title' => 'London',
    'population' => '8674000'
]);
echo $london->population; // 8.674M
    
$reykjavik = City::insert([
    'title' => 'reykjavik',
    'population' => '119200'
]);
echo $reykjavik->population; // 119.2K