[Nolug] php: list sorting algorithm help

I need an algorithm to sort a list in the following way (in php):

List (unsorted) is as follows:
        1 / 0
        2 / 1
        8 / 1
        3 / 2
        7 / 2
        4 / 3
        5 / 3
        6 / 3
        9 / 8
        10/ 9

The list should end up like this:
        1 / 0
        --2 / 1
        ----3 / 2
        ------4 / 3
        ------5 / 3
        ------6 / 3
        ----7 / 2
        --8 / 1
        ----9 / 8
        ------10/ 9

The first field is a unique ID, the second is an association with some
other entry in the list. This allows topics and subtopics (represented
above with dashes) of infinite levels to be contained in the same list
(there are reasons I need this).

I have been struggling with this. I think I am at the limit of my
programming prowess. Can anybody help, or give me the crucial pointer
in the right direction?
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Received on 12/23/03