title: Python sum value in Data Frame for each country and keep PopData
body: <p>I am new into Python and stuck within the following task: This is my Data Frame</p>
  
  <pre><code>countriesAndTerritories  cases  popData2018
  0                 Afghanistan    113   37172386.0
  1                 Afghanistan    259   37172386.0
  2                 Afghanistan    280   37172386.0
  3                 Afghanistan    285   37172386.0
  4                 Afghanistan    369   37172386.0
                        ...    ...          ...
  17153                Zimbabwe      0   14439018.0
  17154                Zimbabwe      0   14439018.0
  17155                Zimbabwe      0   14439018.0
  17156                Zimbabwe      1   14439018.0
  17157                Zimbabwe      1   14439018.0
  </code></pre>
  
  <p>I want to sum the amount of all cases per <strong>country</strong> and add the popdata for each country. I tried it via groupby (first without the popdate) and wanted to connect it with a dictionary which includes the information country:popdata. But it didnt worked, because the aggregated result was a series and I couldnt transform it with df.to_frame(). </p>
  
  <p>Do you guys have any ideas about that? My brain is melting already :D</p>
  
  <p>greetz</p>