title: Get proportion of each element of a group by (python)
body: <p>I would like to make a graph to show the proportion p of each element of a <code>df.groupby</code> result.</p>
  <p>My data looks like this: <img src="https://i.stack.imgur.com/cNE9o.png" alt="" /></p>
  <p>I would like to display a bar plot, using the <code>df_country</code> data.</p>
  <p>for the country CH : p = 920/tot, DE : p = 3/tot, US : p= 287 321/ tot</p>
  <p>with tot = sum of all elements : 920 + 3 + 287 321 = 288 244</p>
  <p>I need to do the same with <code>df_unit</code>. Do I need a loop to do this, or can a simple function help me ?</p>