This Code to flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].

PHP - Flat Array

<?php

/**
 * @param array $array
 * @return array Array in fal
 */
function flat(Array $array){
  $result = [];
  foreach($array as $item){
    if(is_array($item)){
      $result = array_merge($result, flat($item));
    }else{
      $result[] = $item;
    }
  }
  return $result;
}