<?php
   function getValue($key, $arr, $default=null) {
       $pieces = explode('.', $key);
       $array = $arr;
       
       foreach($pieces as $array_key) {
       	
          if(!is_null($array) && is_array($array) && array_key_exists($array_key, $array)) { 
              $array = $array[$array_key];
          }
          else {
              $array = null;
              break;
          }
       }
       return is_null($array) ? $default : $array;
   }
   
   $testarr = [
   	    ['foobar' => 'baz'],
   	    ['active' => false]
   	];
   $output = getValue('0.foobar',$testarr,'NOT FOUND');
   var_dump($output);
   $output = getValue('0',$testarr,'NOT FOUND');
   var_dump($output);
   $output = getValue('1.active',$testarr,'NOT FOUND');
   var_dump($output);
   $output = getValue('i.do.not.exist',$testarr,'NOT FOUND');
   var_dump($output);