I really liked your solution. It simple, clear and easy to understand.
It is not part of my original request but is it possible to change the sorting of the ids, so it will keep the same order, without depending on the lexicography order?
If so, what change in code should I do?
The only thing that comes to my mind, is to add a third field to each id that will represent the index. I don't care about the sibling's order, but it will be nice to see an order of parent-chlid.
For example, if we have the following input:
5,#,A
1,5,B
4,5,C
2,4,D

[download]
The output should be: 
A
B,A
C,A
D,C,A

[download]
and not the following output: 
B,A
D,C,A
C,A
A

[download]
Please note that it does not matter for me the order of the sibling.
Thank you for your help! :)

In reply to Re^4: Reorganizing the content of a file by ovedpo15
in thread Reorganizing the content of a file by ovedpo15

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