human
I wrote the below code

    _check_is_partition([row_levels, column_levels], range(ss.index.nlevels))
    values = ss._data.internal_values()._valid_sp_values
    nonnull_labels = ss.dropna()
    def get_indexers(levels):
        '    Return    sparse    coords    and    dense    labels    for    subset    levels    '
        values_ilabels = [tuple((x[i] for i in levels)) for x in nonnull_labels.index]
        if (len(levels) == 1):
            values_ilabels = [x[0] for x in values_ilabels]
        def _get_label_to_i_dict(labels, sort_labels=False):
            '    Return    OrderedDict    of    unique    labels    to    number.\n                                                Optionally    sort    by    label.\n                                                '
            labels = Index(lmap(tuple, labels)).unique().tolist()
            if sort_labels:
                labels = sorted(list(labels))
            d = OrderedDict(((k, i) for (i, k) in enumerate(labels)))
            return d
        def _get_index_subset_to_coord_dict(index, subset, sort_labels=False):
            def robust_get_level_values(i):
                try:
                    return index.get_level_values(index.names[i])
                except KeyError:
                    return index.get_level_values(i)
            ilabels = list(zip(*[robust_get_level_values(i) for i in subset]))
            labels_to_i = _get_label_to_i_dict(ilabels, sort_labels=sort_labels)
            labels_to_i = Series(labels_to_i)
            if (len(subset) > 1):
                labels_to_i.index = MultiIndex.from_tuples(labels_to_i.index)
            labels_to_i.index.names = [index.names[i] for i in subset]
            labels_to_i.name = 'value'
            return labels_to_i
        labels_to_i = _get_index_subset_to_coord_dict(ss.index, levels, sort_labels=sort_labels)
        i_coord = labels_to_i[values_ilabels].tolist()
        i_labels = labels_to_i.index.tolist()
        return (i_coord, i_labels)
    (i_coord, i_labels) = get_indexers(row_levels)
    (j_coord,...

What's a good function header?
 ... Here's a good function header?
assistant
#Here's a good function header.

def _to_ijv(ss, row_levels=(0,), column_levels=(1,), sort_labels=False):