title: ValueError: cannot convert float NaN to integer
body: <p>I am writing a function that returns a dictionary with the year of the docs as key and, as value, it specifies a tuple that is returned by def do_get_citations_per_year function.</p>
  
  <p>This function processes the df:</p>
  
  <pre><code>def do_process_citation_data(f_path):
      global my_ocan
  
      my_ocan = pd.read_csv(f_path, names=['oci', 'citing', 'cited', 'creation', 'timespan', 'journal_sc', 'author_sc'],
                            parse_dates=['creation', 'timespan'])
      my_ocan = my_ocan.iloc[1:]  # to remove the first row
      my_ocan['creation'] = pd.to_datetime(my_ocan['creation'], format="%Y-%m-%d", yearfirst=True)
      my_ocan['timespan'] = my_ocan['timespan'].map(parse_timespan)
      #print(my_ocan.info())
      print(my_ocan['timespan'])
      return my_ocan
  </code></pre>
  
  <p>Then I have this function, when running it it does not trigger any error:</p>
  
  <pre><code>    result = tuple()
      my_ocan['creation'] = pd.DatetimeIndex(my_ocan['creation']).year
  
      len_citations = len(my_ocan.loc[my_ocan["creation"] == year, "creation"])
      timespan = round(my_ocan.loc[my_ocan["creation"] == year, "timespan"].mean())
      result = (len_citations, timespan)
      print(result)
  
  
      return result
  </code></pre>
  
  <p>When I run that function inside of another function:</p>
  
  <pre><code>def do_get_citations_all_years(data):
      mydict = {}
      s = set(my_ocan.creation)
      for year in s:
          mydict[year] = do_get_citations_per_year(data, year)
  
      return mydict
  </code></pre>
  
  <p>I get the error:</p>
  
  <pre><code>  File "/Users/lisa/Desktop/yopy/execution_example.py", line 28, in &lt;module&gt;
      print(my_ocan.get_citations_all_years())
    File "/Users/lisa/Desktop/yopy/ocan.py", line 35, in get_citations_all_years
      return do_get_citations_all_years(self.data)
    File "/Users/lisa/Desktop/yopy/lisa.py", line 112, in do_get_citations_all_years
      mydict[year] = do_get_citations_per_year(data, year)
    File "/Users/lisa/Desktop/yopy/lisa.py", line 99, in do_get_citations_per_year
      timespan = round(my_ocan.loc[my_ocan["creation"] == year, "timespan"].mean())
  ValueError: cannot convert float NaN to integer
  </code></pre>
  
  <p>What can I do to solve the issue? </p>
  
  <p>Thank you in advance</p>