code: def group_concat(arg, sep=',', where=None):
      
      return ops.GroupConcat(arg, sep, where).to_expr()
docs: Concatenate values using the indicated separator (comma by default) to
      produce a string
  
      Parameters
      ----------
      arg : array expression
      sep : string, default ','
      where : bool, default None
  
      Returns
      -------
      concatenated : string scalar