def append_column(self, data_array, ckey='temp'):
        """
        This will append a new column and fill it with the data from the
        the supplied array.
        
        Parameters
        ----------
        data_array  
            Data; can be a list, but will be converted to numpy array
        ckey        
            Name of the column.
        """
        if not type(ckey) is str:
            print("ERROR: ckey should be a string!")
            return

        if ckey in self.ckeys:
            print("ERROR: ckey '"+ckey+"' already exists!")
            return

        return self.insert_column(data_array, ckey)