This dataframe can be converted into a repgrid object via importDataframe(). The dataframe column names are the
minimum of the rating scale (1), the element names (element_1 to element_4), the maximum of the rating scale
(5), and optionally a column indicating the preferred pole. Each row contains the constructs' entries (left
pole, ratings, right pole, preferred pole). The preferred pole must be one of left, right, none, NA (see
preferredPoles()). See sample data df_element_columns.