title: list inside pandas dataframe cells
body: <p>I have a data-frame like this:</p>
  
  <p><a href="https://i.stack.imgur.com/gv25n.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gv25n.png" alt="enter image description here"></a></p>
  
  <p>and I want a new data-frame  with a new column which contains a list like this: 
  <a href="https://i.stack.imgur.com/GxvbI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GxvbI.png" alt="enter image description here"></a></p>
  
  <p>How do I create a list inside a data-frame cell which contains the elements based on similar month?</p>