title: Create stack of array from existing array
body: <p>Let's say I have an array like this:</p>
  
  <pre><code>$mail[0] = "test1@gmail.com";
  $mail[1] = "test2@gmail.com";
  $mail[2] = "test3@gmail.com";
  $mail[3] = "test4@gmail.com";
  $mail[4] = "test5@gmail.com";
  $mail[5] = "test6@gmail.com";
  </code></pre>
  
  <p>Now I want to convert these mails to string and put them in array after every 3 mail of $mail separated by a comma.
  Something like this - </p>
  
  <pre><code>$email[0] = "test1@gmail.com, test2@gmail.com, test3@gmail.com";
  $email[1] = "test4@gmail.com, test5@gmail.com, test6@gmail.com";
  $email[2] = "test71@gmail.com, test8@gmail.com, test9@gmail.com";
  </code></pre>
  
  <p>How can I do this ?</p>