title: how to append a dataframe to existing csv file and remove the duplicates data
body: <p>i have a dataframe data and csv data as following
  <a href="https://i.stack.imgur.com/9dfa1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9dfa1.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/dmoWD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dmoWD.png" alt="enter image description here"></a></p>
  
  <p>i want to append the dataframe data to the csv file.however ,there are duplicates  between the two data.so how to remove the duplicates and append new data to csv file.</p>