title: Select equal values from one column, with different values in second column
body: <p>I have a large dataframe in R looking like this:</p>
  
  <p>BCountry  BNr</p>
  
  <p>DE        1 </p>
  
  <p>DE        1</p>
  
  <p>DE        1</p>
  
  <p>FR        2  </p>
  
  <p>FR        2</p>
  
  <p>PL        2</p>
  
  <p>How can I exclude all rows, where the B.Nr is equal, but the BCountry is not.
  So my desired result would be</p>
  
  <p>BCountry BNr</p>
  
  <p>FR       2 </p>
  
  <p>FR       2</p>
  
  <p>PL       2</p>
  
  <p>I appreciate any help :))</p>