title: Pandas plot mean values from corresponding unique id values
body: <p>This is my csv file. I want to find the mean cost for each unique ids. </p>
  
  <p>so for example: id 1, mean cost should be 20.</p>
  
  <pre><code>id,cost
  1,10 
  1,20
  1,30
  2,40
  2,50
  </code></pre>
  
  <p>I got the output right with:</p>
  
  <pre><code>df.groupby(['id'])['cost'].mean()
  id
  1    20
  2    45
  Name: cost, dtype: int64
  </code></pre>
  
  <p>But i dont know how to plot such that x-axis is the id (1,2) and y axis as the mean values (20,45). </p>
  
  <p>The below code made the mean to be the x-axis (should be on y-axis) while the y-axis is only until 1 (should be 2 and should be the x-axis). </p>
  
  <pre><code>df.groupby(['id'])['cost'].mean().hist()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/tpP7j.png" rel="nofollow"><img src="https://i.stack.imgur.com/tpP7j.png" alt="enter image description here"></a></p>