Read date-value table.

def r_date_num(obj, multiple=False):
    """Read date-value table."""
    if isinstance(obj, (list, tuple)):
        it = iter
    else:
        it = LinesIterator
    if multiple:
        datasets = {}
        for line in it(obj):
            label = line[2]
            if label not in datasets:
                datasets[label] = Dataset([Dataset.DATE, Dataset.FLOAT])
                datasets[label].name = label
            datasets[label].parse_elements(line[0:2])
        return datasets.values()
    dataset = Dataset([Dataset.DATE, Dataset.FLOAT])
    return dataset.load(it(obj))