title: How can i remove repeated values in a single column?
body: <p>i have a dataframe like:</p>
  <pre><code>shops        prod_id      atv_y1   
  
  company_b    A           56.3      
  company_b    B           4.3     
  company_b    C           136.3    
  company_b    D           89.3
  company_c    A           7.3
  company_c    B           64.0 
  company_c    A           34.7    
  </code></pre>
  <p>For the purpose of plotting i would like to remove the repeated company_b/company_c values so that it takes only the first time it is referenced like below:</p>
  <pre><code>shops        prod_id      atv_y1   
  
  company_b    A           56.3      
               B           4.3     
               C           136.3    
               D           89.3
  company_c    A           7.3
               B           64.0 
               A           34.7  
  </code></pre>
  <p>how can i do this in pandas ?</p>