@classmethod
def length(cls, dataset):
    """
        Returns the length of the multi-tabular dataset making it appear
        like a single array of concatenated subpaths separated by NaN
        values.
        """
    if not dataset.data:
        return 0
    length = 0
    ds = cls._inner_dataset_template(dataset)
    for d in dataset.data:
        ds.data = d
        length += ds.interface.length(ds)
    return length + len(dataset.data) - 1
