test.php

<?php

//import apalah disini

class X extends REST_Controller{
  public function index_get(){
   //Get lapangan
    $lapangan = $this->m_futsal->lapangan()->result();
    $tersedia = $this->m_futsal->tersedia();
    
    //tempat sementara
    $lapangannya = [];
    
    //Loop Lapangan
    foreach($lapangan as $lapanganF){
      foreach($tersedia as $tersediakan){
        if($tersediakan["id_lapangan"] != $lapanganF["id_lapangan"] && $tersediakan["id_futsal"] != $lapanganF["id_futsal"]){
          array_push($lapangannya, $lapanganF["id_lapangan"];
        }
      }
    }
                     
    echo "Lapangan yang tersedia : ". implode(", ", $lapangannya);
    
  }
}