title: understanding level =0 and group_keys
body: <p>I am using pandas groupby and finding size for ex:</p>
  
  <pre><code>dd=df.groupby(['value','year','team']).size()
  </code></pre>
  
  <p>and it giving me output as:</p>
  
  <pre><code>value  year  team
  0      2000  B       2
  1      2000  A       2
         2001  A       1
  2      2001  B       1
  3      2001  A       2
  </code></pre>
  
  <p>my question is what is level =0 and group_keys (given below )which is applying on grouped dataframe dd.</p>
  
  <pre><code>ddf3=dd.groupby(level=0,group_keys=False).apply(function).reset_index()
  </code></pre>
  
  <p>is (level=0) be 'value' column in grouped dataframe dd.</p>
  
  <p>Please help me. </p>