[pygtk] Sorting every row of a tree regardless of its hierarchy

[John Finlay]

Jiri Bajer wrote:
> On Wed, 2009-08-26 at 01:47 +0200, John Finlay wrote:
>   
>>> If I store the data in a TreeModel, wrap a TreeModelSort over it and
>>> display the result via TreeView, the sorting mechanism is not able to
>>> put "Task 2" before "Task 1.2" even if "Task 2" has higher priority. It
>>> is caused by respecting the hierarchy - sorting won't break a child from
>>> its parent (but I need to do so).
>>>
>>> Is there any way how to achieve such sorting without maintaining two
>>> copies of all data - one in TreeStore and one in ListStore and
>>> sorting/displaying the ListStore instead?
>>>   
>>>       
>> Look at the TreeModelFilter. With the right set_modify_func() function 
>> you may be able to massage the look for your purposes.
>>     
>
> Thanks for a hint! I've managed to create a 1:1 mapping between filtered
> and original model - but I don't see how to change the row hierarchy in
> the filtered model. It seems to me it is not possible to do anything
> else than setting a value for filtered model's cell and thus using
> PyGTK's native tree sorting mechanism over the filtered model won't
> work.
>
> Did you mean I can reorder the filtered tree rows as if they were sorted
> by a given column (with original model's hierarchy that doesn't respect
> my re-ordering) and then hide the expanders? That would also mean I have
> to maintain a path-to-path/row-to-row mapping for every tree row and
> every column I want to sort-by.
>
> Mapping example for sort by Priority:
>
> tree -> sorted "flat" list
> (0,) -> (0,)
> (0,0) -> (1,)
> (0,1) -> (3,)
> (1,) -> (2,)
>
> Do you have any tips for the mapping? If I use something like the
> example before I have to go through most of the tree and re-number the
> paths with every row insert/delete (but finding the right path is easy).
>
> Or I could store "pointers" like iterators or row references for every
> row and every sortable column - they wouldn't need any additional care
> in case of row insert/delete. But the iterators are not guaranteed to be
> persistent and large number of row references would slow down the tree
> to crawl...
>
> That looks like having two copies of all data (a tree and a list)
> doesn't help either because I would have to maintain the path-to-path
> mapping anyway (or compute it on a fly by walking through all tree rows,
> counting the rows traversed and searching for a particular hierarchy
> number - which is too slow, O(N) for N=number of tree rows).
>
> I can also imagine a hybrid solution where every parent tree node keeps
> a number of nodes in his subtree which would speed up the tree
> traversing to something like O(log N) but would also add O(log N)
> operation of re-calculating the counts in a part of subtree on every row
> add/delete.
>
> >From what I've thought about so far it seems the easiest way would be to
> hack into the TreeModelSort and add a property that would control if the
> rows compared during the sort operation will respect the hierarchy or if
> every row in the model gets compared. Can it be done directly from
> Python or will I have to roll up the sleeves and dive into the C code?
> Are there any tutorials available?
>
> Thanks for any further ideas!
>
>   
I think that you have to use a ListStore instead of a TreeStore and then 
work out some way to simulate a hierarchy with hiding "children" which I 
imagine is the major benefit of using a TreeStore. I was thinking a 
TreeModelFilter could do this.

John