title: TypeError: 'Series' objects are mutable, thus they cannot be hashed problemwith column
body: <p>I have a problem with a column of my dataframe but I don't understand why there are trouble on my column cat.<a href="https://i.stack.imgur.com/rDlmH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rDlmH.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/u16hs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/u16hs.png" alt="enter image description here"></a></p>