title: Error 'numpy.int32' object does not support item assignment
body: <p>I get this error </p>
  
  <pre><code>Traceback (most recent call last):
  File "C:\Users\User1\Desktop\cellh5_scripts\ewa_pnas_fate.py", line 90,     in &lt;module&gt;
  ec.combine_classifiers("Event labels combined")
  File "C:\Users\User1\Desktop\cellh5_scripts\ewa_pnas_fate.py", line 53, in combine_classifiers
  pnas_class[pnas_class==3] = 1
  TypeError: 'numpy.int32' object does not support item assignment
  </code></pre>
  
  <p>by runing the code</p>
  
  <pre><code>def combine_classifiers(self, output_name):
      all_combined_classes = []
      for _, (plate_name, w, p, t1, t2, track_ids, track_labels) in self.mapping[['Plate', 
                                                                          'Well', 
                                                                          'Site', 
                                                                          'Gene Symbol',
                                                                          'siRNA ID', 
                                                                          'Event track ids',
                                                                          'Event track labels']].iterrows(): 
          combined_classes = []
          ch5_file_handle = self.cellh5_handles[plate_name]
          ch5_pos = ch5_file_handle.get_position(w, str(p))
  
  
  
          for track_id, track_label in zip(track_ids, track_labels):
  
              h2b_class = track_label.copy()
              print(track_id)
              pnas_class = ch5_pos.get_class_prediction('secondary__expanded')[track_id]['label_idx'] + 1
              print(pnas_class)
  
  
              inter_idx = h2b_class == 1 
              pnas_class[pnas_class==3] = 1
              pnas_class[pnas_class==2]+=2
              combined_class = h2b_class
              combined_class[inter_idx] = pnas_class[inter_idx] 
              combined_classes.append(combined_class)
  
          all_combined_classes.append(combined_classes)
  
      self.mapping[output_name] = pandas.Series(all_combined_classes) 
  </code></pre>
  
  <p>I print pnas_class which is 1, and track_id which is 50708. I'm wondering what the designer of code want to do in the part:</p>
  
  <pre><code>inter_idx = h2b_class == 1 
  pnas_class[pnas_class==3] = 1
  pnas_class[pnas_class==2]+=2
  combined_class = h2b_class
  combined_class[inter_idx] = pnas_class[inter_idx] 
  </code></pre>
  
  <p>How can I change that to have the same meaning?</p>