ctrie-java
RoaringBitmap
ctrie-java | RoaringBitmap | |
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1 | 24 | |
1 | 3,388 | |
- | 0.8% | |
10.0 | 8.5 | |
almost 4 years ago | 10 days ago | |
Java | Java | |
Apache License 2.0 | Apache License 2.0 |
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ctrie-java
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Ask HN: What are some 'cool' but obscure data structures you know about?
Concurrent tries with non-blocking snapshots [0]
Say that you have a dataset that needs to be ordered, easily searchable, but is also updated quite frequently. Fast accesses are a pain if you decide to use traditional read-write locks.
Ctries are entirely lock-free, thus there is no waiting for your read operations when an update is happening, i.e. you run lookups on snapshots while updates happen.
They are also a lot of fun to implement, especially if you aren't familiar with lock-free algorithms! I did learn a lot doing it myself [1]
[0] http://aleksandar-prokopec.com/resources/docs/ctries-snapsho...
[1] https://github.com/mabeledo/ctrie-java
RoaringBitmap
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Iterating over Bit Sets Quickly
I was recently reading about Roaring https://roaringbitmap.org/ which is a highly optimized compressed bitset implementation. I reccomend reading about it if you are interested in this sort of thing. The talk at https://roaringbitmap.org/talks/ is especially good.
- Roaring Bitmaps
- Roaring bitmaps are compressed bitmaps, can be 100x faster
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What feature would you like to remove in C++26?
However, I would love compressed (not just packed) bitsets too, which is something different to me. I would make it another class with a similar interface, based on something like roaring. It doesn't need to be in the standard, but it would be nice if the API was a such that one could easily swap implementations.
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Jaccard Index
As an aside if you find yourself having to compute them on the fly, know that the Roaring Bitmaps libraries is the way to go [1]. The bitmaps are compressed, and can be streamed directly into SIMD computations (batching XORs and popcnts 256 bits wide!). The Jaccard index is just intersection_len / union_len [2] away
[1] https://roaringbitmap.org/
[2] https://roaringbitmap.readthedocs.io/en/latest/#roaringbitma...
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Looking for fast, space-efficient key-lookup
Use a two stage approach, with a bloom/cuckoo filter stored as a https://roaringbitmap.org/ in memory. Then a secondary key/value store on disk (bolt or anything else).
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BitSet Vs BigInteger
As an aside, if you're dealing with large bit sets, you might also want to evaluate Roaring Bitmaps.
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Negative Incentives in Academic Research
Sidetracking a bit the conversation. What a coincidence that the author (Lemire) is also represented on Today's #1 "Ask HN: What are some cool but obscure data structures you know about?" as he is the main contributor of RoaringBitmap https://github.com/RoaringBitmap/RoaringBitmap and one of the main authors of the data structure.
- Ask HN: What are some 'cool' but obscure data structures you know about?
- Roaring bitmaps: A better compressed bitset
What are some alternatives?
PSI - Private Set Intersection Cardinality protocol based on ECDH and Bloom Filters
HyperMinHash-java - Union, intersection, and set cardinality in loglog space
minisketch - Minisketch: an optimized library for BCH-based set reconciliation
lucene - Apache Lucene open-source search software
sdsl-lite - Succinct Data Structure Library 2.0
CQEngine - Ultra-fast SQL-like queries on Java collections
CPython - The Python programming language
Primes - Prime Number Projects in C#/C++/Python
Folly - An open-source C++ library developed and used at Facebook.
Feign - Feign makes writing java http clients easier
us - An alternative interface to Sia
maven-compiler-plugin - Apache Maven Compiler Plugin