title: remove not matching rows from a df by checking in another df
body: <p>I have 2 data frames. I want to remove items from the second data frame which is not present in the first data frame.</p>
  <p>df1</p>
  <pre><code>a  
  
  tom
  mat
  stuart
  </code></pre>
  <p>df2</p>
  <pre><code>b
  
  tom
  mat
  max
  </code></pre>
  <p>Expected df after removing not matching value of b from a :</p>
  <p>df1</p>
  <pre><code>a  
  
  tom
  mat
  stuart
  </code></pre>
  <p>df2</p>
  <pre><code>b
  
  tom
  mat
  
  </code></pre>