code: def unique_reactions(df):
      
      reaction_list =[]
      for idx, entry in enumerate(df['reactants']):
          reaction = []
          for x in entry:
              reaction.append(x)
          reaction.append('-->')
          for y in df['products'][idx]:
              reaction.append(y)
          reaction_list.append(reaction)
      string_list = [str(reaction) for reaction in reaction_list]
      string_list = sorted(list(set(string_list)))
      reaction_list = [ast.literal_eval(entry) for entry in string_list]
      return(reaction_list)
docs: Identifies unique elementary reactions in data frame.
  
      Parameters
      ----------
      df : Data frame.
  
      Returns
      -------
      reaction_list : List of unique elementary reactions.