code: def diffm(self, diffcol: str, name: str="Diff", default=nan):
          
          try:
              df = self.df.copy()
              mean = self.df[diffcol].mean()
              vals = []
              for _, row in self.df.iterrows():
                  num = row[diffcol]
                  if num > 0:
                      diff = int(((num - mean) * 100) / mean)
                      vals.append(diff)
                  else:
                      vals.append(default)
              self.df = df
              self.add(name, vals)
          except Exception as e:
              self.err(e, self._append, "Can not diff column")
              return
          self.ok("Diff column " + name + " added to the dataframe")
docs: Add a diff column to the main dataframe: calculate the
          diff from the column mean
  
          :param diffcol: column to diff from
          :type diffcol: str
          :param name: diff column name, defaults to "Diff"
          :param name: str, optional
          :param default: column default value, defaults to nan
          :param default: optional
  
          :example: ``ds.diffm("Col 1", "New col")``