ekmett / succinct

playground for working with succinct data structures

succinct

This is a playground for exploring succinct data structures in Haskell

Contact Information

Contributions and bug reports are welcome!

Please feel free to contact me through github or on the #haskell IRC channel on irc.freenode.net.

-Edward Kmett

succinct's Issues

Implement forwardSearch and backwardSearch

The RangeMin tree is based on the ideas from Fully-Functional Succinct Trees by Sadakane and Navarro.

However, I only store the minima rather than both minima and maxima, based on an observation in Fast Compressed Tries through Path Decompositions by Grossi and Ottaviano.

I also store the encoding of the minima as a delta in order to get a proper monoid.

Since the structure I have is trivially isomorphic to Grossi and Ottaviano's, it should be capable of supporting fwd-search and bwd-search which is necessary for fast balanced-parentheses trees.

Add CSPoppy

@moritayasuaki has an implementation of it forked off of my structures repository at:

https://github.com/moritayasuaki/structures/blob/succinct/src/Data/Vector/Succinct/Poppy.hs

Implement Rank9 and Select9

http://sux.di.unimi.it/paper.pdf

NB: what we currently call Rank9 is a gross oversimplification that takes 2n space while real Rank9 takes 1.25n.

How to index a tree that stores elements at each node?

Let's assume that I have something like Tree from Data.Tree in containers and I want to efficiently navigate this tree using a zipper into a compressed index to retrieve elements from the tree. My rough understanding is that the way I would do this is:

1. Define my own function from Tree to Succinct.Tree.LOUDS.Rose that just extracts the tree's skeleton
2. Compute a Rank9 index from my Rose-encoded skeleton using Succinct.Tree.LOUDS.fromRose
3. Store the index alongside an array containing the tree elements in some order. I'm guessing they would be stored in level order (for LOUDS), but I'm not totally sure.
4. When it's time to retrieve an element, wrap the Rank9 index in a Zipper using root so I can navigate the skeleton of the tree without materializing it using all the zipper operations
5. After I navigate to some node, I need to retrieve the index into my array of elements. This is the part I don't know how to do since I'm not sure how I retrieve that index from the Zipper. I read the documentation for Zipper but it's still pretty unclear to me if one of the two Int fields is the index or not.

So basically I need help with steps 3 and 5: what order do I store the array of elements and how do I retrieve the index into the array from the Zipper?

Implement Elias delta-coded Gap Encoding

Rank and select revisited and extended

Bitvectors polymorphic in underlying Vector type

Currently the bitvectors in succinct are represented by Data.Vector.Unboxed Vectors. Allowing bitvectors of any Vector type would, among other things, enable easy disk backing of succinct structures (with an mmap'd Storable vector).

I have a first cut at this generalization in my generalize-vector branch. This isn't a pull request as I'm not entirely pleased with how intrusive this change is as it sits. I've tried to preserve the existing monomorphic interfaces for ease of use by building them on top of polymorphic primed variants (e.g. Rose).

Implement Poppy

http://www.cs.cmu.edu/~dongz/papers/poppy.pdf

This would be more space (and time) efficient than Rank9.

Reintroduce inlines

Investigate the issue that prompted 7b44e6d, maybe it was caused by a trivial bug:

When I reintroduced the inlines on the rank1 and rank0 methods in the Ranked class, it triggered the 'simplifier ticks exhausted'. But, I noticed that the definitions were bogus:

rank1 t i = i - rank1 t i

Instead of rank0 and rank1 being defined in terms of each other. When I fixed this, the simplifier wasn't exhausted anymore. :)

Oh, and if this really was the cause, then this should be fixed in GHC!

Buggy Zippers

Somewhere along the way I changed an implementation detail and appear to have broken the tree zippers.

Build is broken.

Is it still maintained?