title: How to make an array of arrays in kotlin?
body: <p>I have an array of userIDs, which contains specific users from a certain group.</p>
  <p>{userID1,userID2}</p>
  <pre><code>val userIDArrayList: ArrayList&lt;String&gt; = ArrayList()
      userIDArrayList.add(userID1)
      userIDArrayList.add(userID2)
  </code></pre>
  <p>I want to make a master array which contains several different user arrays.</p>
  <p>[{userID1, userID2}, {userID3, userID4}]</p>
  <p>How can I do that in kotlin?</p>