title: how to pluck email from array of users
body: <p>If I do <code>User.all.pluck(:email)</code> then it works fine.</p>
  
  <p>But if I do </p>
  
  <pre><code>arr = Array.new
  arr = User.all
  </code></pre>
  
  <p>and then</p>
  
  <pre><code>arr.pluck(:email)
  </code></pre>
  
  <p>this is raising following error</p>
  
  <pre><code>undefined method `pluck' for #&lt;Array:0x007f4ff8daf3c8&gt;
  </code></pre>
  
  <p>which means I cannot use pluck with arrays, so how can we get particular field value from an array of records in just one line like above.
  <strong>I don't want to loop through each record in an array</strong>.</p>