title: Appending only new values from a dataframe to another dataframe in pandas
body: <p>I have a very huge data frame with me. I have also a small data frame with me.</p>
  
  <p>Both of those data frames will have same columns. </p>
  
  <p>The small data frame will have some rows that are already present in the big data frame. I want to append the small data frame to big one such that there will be no duplicates in the big data frame.</p>
  
  <p>I can append simply and then remove the duplicates. But this will lead to wastage of memory to keep the duplicated data frame in the memory.</p>
  
  <p>Is there any other method that can be used efficiently to solve this.?</p>