title: Check if a row in one data frame exist in another data frame
body: <p>I have a data frame A like this:</p>
  
  <p><a href="https://i.stack.imgur.com/uu12A.png" rel="noreferrer"><img src="https://i.stack.imgur.com/uu12A.png" alt="enter image description here"></a></p>
  
  <p>And another data frame B which looks like this:</p>
  
  <p><a href="https://i.stack.imgur.com/DI78z.png" rel="noreferrer"><img src="https://i.stack.imgur.com/DI78z.png" alt="enter image description here"></a></p>
  
  <p>I want to add a column 'Exist' to data frame A so that if User and Movie both exist in data frame B then 'Exist' is True, otherwise it is False.
  So A should become like this:
  <a href="https://i.stack.imgur.com/sPxfb.png" rel="noreferrer"><img src="https://i.stack.imgur.com/sPxfb.png" alt="enter image description here"></a></p>