`transition_slices_from_group`

[chaburkland]

Using internal ArrayKit utilities, and avoiding the usage of Python objects where possible, lets implement transition_slices_from_group as CPythhon function in ArrayKit.

def _slices_from_transitions(
    transitions: tp.Iterator[int], size: int
) -> tp.Iterator[slice]:
    start = 0
    for t in transitions:
        yield slice(start, t)
        start = t

    if start < size:
        yield slice(start, None)


def transition_slices_from_group(group: np.ndarray) -> tuple[tp.Iterator[slice], bool]:
    if group.ndim == 2:
        group_to_tuple = True
        if group.dtype == DTYPE_OBJECT:
            # NOTE: cannot get view of object; use string
            consolidated = view_2d_as_1d(group.astype(str))
        else:
            consolidated = view_2d_as_1d(group)
        transitions = nonzero_1d(consolidated != roll_1d(consolidated, 1))[1:]
    else:
        group_to_tuple = False
        transitions = nonzero_1d(group != roll_1d(group, 1))[1:]

    return _slices_from_transitions(transitions, len(group)), group_to_tuple  # type: ignor

See comment: static-frame/static-frame#1078 (comment)