title: How can I drop obs. conditionally to another data frame? R
body: <p>Ok, so I have my dataset for firms that seems like this</p>
  <p>There are 98688 firms that are shown 6 years</p>
  <p>So this data base is</p>
  <p><code>Balances</code></p>
  <pre><code>Year     FirmID      Sales
  2014       A101        3 
  2015       A101        5
  2016       A101        2
  2017       A101        1
  2018       A101        3
  
  2014       B107        3 
  2015       B107        5
  2016       B107        2
  2017       B107        1
  2018       B107        3
   .          .          .
   .          .          .
   .          .          .
   .          .          .
  </code></pre>
  <p>And I have a list that I need to get rid off that list is just like this</p>
  <p><code>Sacar</code></p>
  <pre><code>FirmID    Sacar
  A101      sacar
  B107      sacar
  .         sacar
  .         sacar
  .         sacar
  </code></pre>
  <p>How would you do it?</p>
  <p>I was trying with a left join and then a filter</p>