title: Array keys ,get array values ,then comma separate
body: <p>I have :</p>
  
  <pre><code>$a = array(
      0=&gt;'you',
      1=&gt;'will',
      2=&gt;'be',
      3=&gt;'so',
      4=&gt;'happy',
      5=&gt;'in'
  );
  
  $b = array(
      0=&gt;'1',
      1=&gt;'4',
      2=&gt;'5'
  );   // (KEYS:1,4,5)
  </code></pre>
  
  <p>I want out the values of $a that matches $b's keys;</p>
  
  <p>so $val would be <code>willhappyin</code>.</p>
  
  <p>And then comma-separate them.. like: <code>will,happy,in</code> without comma after last one.</p>
  
  <p>How can i do this ? :)   </p>