title: Determine if a tibble is grouped or not
body: <p>Is there a function to determine if a tibble is a grouped one or not.</p>
  
  <p>I use the following code to create an aggregated variable without shrinking the dataset:</p>
  
  <pre><code>mydataset %&gt;% select(count, group) %&gt;%
    group_by(group) %&gt;%
    mutate(count_group = sum(count))
  </code></pre>
  
  <p>If I use mutate, I have a grouped tibble. If I use summarise, I have a simple tibble.</p>
  
  <p>Is there a function, like <code>as.grouped()</code> which allows to determine the character grouped of a tibble?</p>