Sorting x lists based on one list ... maybe an example would make sense:

[Philippe C. Martin]

> Another way would be to merge the three lists into one of 3-tuples, sort,
> and unmerge, similarly to the DSU pattern -- which raises the question:
> why are you using three lists in the first place?

:-) Thanks, the lists will evolve and are also stored in 'csv' format in
external files at one point. I cannot use dictionaries because I need to
control the sorting (hash).

In this specific case, list 1 represents students with their information,
list 2 represents assignments with information such as weight, term, max
grade ... and list 3 the actual grades.

Regards,

Philippe



Peter Otten wrote:

>> Philippe C. Martin wrote:
>> 
>>> I'm looking for an easy algorithm - maybe Python can help:
>>> I start with X lists which intial sort is based on list #1.
>>> I want to reverse sort list #1 and have all other lists sorted
>>> accordingly.
> 
> One way, using a helper list with indices:
> 
>>>> l1 = ['a','b','c']
>>>> l2 = ['toto','titi','tata'] # 'toto' refers to 'a', 'titi' to b' ....
>>>> l3 = ['foo','bar','doe'] # 'foo' refers to 'a' ........
>>>> indices = sorted(range(len(l1)), key=l1.__getitem__, reverse=True)
>>>> for items in l1, l2, l3:
> ...     items[:] = [items[i] for i in indices]
> ...
>>>> l1
> ['c', 'b', 'a']
>>>> l2
> ['tata', 'titi', 'toto']
>>>> l3
> ['doe', 'bar', 'foo']
> 
> Another way would be to merge the three lists into one of 3-tuples, sort,
> and unmerge, similarly to the DSU pattern -- which raises the question:
> why are you using three lists in the first place?
> 
> Peter