code: def write_to(self, group, append=False):
          
          if self.sparsetodense:
              self.data = [x.todense() if sp.issparse(x) else x
                           for x in self.data]
  
          nframes = sum([d.shape[0] for d in self.data])
          dim = self._group_dim(group)
          feats = np.concatenate(self.data, axis=0)
  
          if append:
              nframes_group = group[self.name].shape[0]
              group[self.name].resize(nframes_group + nframes, axis=0)
              if dim == 1:
                  group[self.name][nframes_group:] = feats
              else:
                  group[self.name][nframes_group:, :] = feats
          else:
              group[self.name].resize(nframes, axis=0)
              group[self.name][...] = feats if dim == 1 else feats
docs: Write stored features to a given group