def left_join(input, **params):
    """
    Left join transformation
    :param input:
    :param params:
    :return:
    """
    PARAM_COL_RIGHT = 'col.right'
    PARAM_COL_LEFT = 'col.left'
    PARAM_FIELD_JOIN = 'field.join'

    right_df = pd.DataFrame.from_records(input[params.get(PARAM_COL_RIGHT)])
    left_df = pd.DataFrame.from_records(input[params.get(PARAM_COL_LEFT)])
    join_on = params.get(PARAM_FIELD_JOIN)
    res = right_df.set_index(join_on, drop=False).join(left_df.set_index(join_on, drop=False), on=[join_on], rsuffix='_right')
    return Converter.df2list(res)