title: Altair - How to create a grouped bar Chart without manipulating the DataFrame
body: <p>I noticed that one can create grouped bar charts in Altair, by evaluating the column of a DataFrame. My issue is that my data doesn't have each group as a value of an specific column.</p>
  <p>So, is it possible to use the column name as a group name in Altair (without evaluating the column) or modifying the DataFrame?</p>
  <h1>Below is the DataFrame I have and the grouped bar chart I need:</h1>
  <p><a href="https://i.stack.imgur.com/5wrBG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5wrBG.png" alt="enter image description here" /></a></p>