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RRB-Trees in Clojure

README.md

core.rrb-vector

An implementation of the confluently persistent vector data structure introduced in Bagwell, Rompf, "RRB-Trees: Efficient Immutable Vectors", EPFL-REPORT-169879, September, 2011.

RRB-Trees build upon Clojure's PersistentVectors, adding logarithmic time concatenation and slicing. ClojureScript is supported with the same API except for the absence of the vector-of function.

The main API entry points are clojure.core.rrb-vector/catvec, performing vector concatenation, and clojure.core.rrb-vector/subvec, which produces a new vector containing the appropriate subrange of the input vector (in contrast to clojure.core/subvec, which returns a view on the input vector).

core.rrb-vector's vectors can store objects or unboxed primitives. The implementation allows for seamless interoperability with clojure.lang.PersistentVector, clojure.core.Vec (more commonly known as gvec) and clojure.lang.APersistentVector$SubVector instances: clojure.core.rrb-vector/catvec and clojure.core.rrb-vector/subvec convert their inputs to clojure.core.rrb_vector.rrbt.Vector instances whenever necessary (this is a very fast constant time operation for PersistentVector and gvec; for SubVector it is O(log n), where n is the size of the underlying vector).

clojure.core.rrb-vector also exports its own versions of vector, vector-of and vec which always produce clojure.core.rrb_vector.rrbt.Vector instances. Note that vector-of accepts :object as one of the possible type arguments, in addition to keywords naming primitive types.

Usage

core.rrb-vector exports one public namespace:

(require '[clojure.core.rrb-vector :as fv])

Note that the ClojureScript version uses the same namespace name (it does not use the alternative cljs.* prefix!). This is because the API is precisely the same (except clojure.core.rrb-vector/vector-of only makes sense on the JVM and is therefore not available in ClojureScript).

The docstring attached to the namespace provides an overview of the available functionality (as found at the top of this README):

(doc clojure.core.rrb-vector)

The new functionality is accessible through two functions: clojure.core.rrb-vector/subvec, which provides logarithmic-time non-view slicing (in contrast to clojure.core/subvec, which is a constant-time operation producing view vectors that prevent the underlying vector from becoming eligible for garbage collection), and clojure.core.rrb-vector/catvec, which provides logarithmic-time concatenation. Crucially, these can be applied to regular Clojure(Script) vectors.

(doc fv/subvec)
(doc fv/catvec)

;; apply catvec and subvec to regular Clojure(Script) vectors
(fv/catvec (vec (range 1234)) (vec (range 8765)))
(fv/subvec (vec (range 1024)) 123 456)

Additionally, several functions for constructing RRB vectors are provided. There is rarely any reason to use them, since, as mentioned above, the interesting functions exported by core.rrb-vector work with regular vectors. Note that clojure.core.rrb-vector/vec, in contrast to clojure.core/vec, reuses the internal tree of its input if it already is a vector (of any type) and does not alias short arrays. When passed a non-vector argument, it returns an RRB vector.

(doc fv/vector)
(doc fv/vector-of)
(doc fv/vec)

The debug namespace bundled with core.rrb-vector provides several utilities used by the test suite, as well as a function for visualizing the internal structure of vectors that works with regular Clojure(Script) vectors and RRB vectors.

;; for peeking under the hood
(require '[clojure.core.rrb-vector.debug :as dv])
(dv/dbg-vec (fv/catvec (vec (range 1234)) (vec (range 8765))))

TODO

  1. more tests;

  2. benchmarks;

  3. performance: general perf tuning, more efficient catvec implementation (to replace current seq-ops-based impl).

Releases and dependency information

core.rrb-vector requires Clojure >= 1.5.0. View vectors created by clojure.core/subvec are correctly handled for Clojure >= 1.6.0. The ClojureScript version is regularly tested against the most recent ClojureScript release.

core.rrb-vector releases are available from Maven Central. Development snapshots are available from the Sonatype OSS repository.

Follow the first link above to discover the current release number.

Leiningen dependency information:

[org.clojure/core.rrb-vector "${version}"]

Maven dependency information:

<dependency>
  <groupId>org.clojure</groupId>
  <artifactId>core.rrb-vector</artifactId>
  <version>${version}</version>
</dependency>

Gradle dependency information:

compile "org.clojure:core.rrb-vector:${version}"

Developer information

core.rrb-vector is being developed as a Clojure Contrib project, see the What is Clojure Contrib page for details. Patches will only be accepted from developers who have signed the Clojure Contributor Agreement.

Clojure(Script) code reuse

core.rrb-vector's vectors support the same basic functionality regular Clojure's vectors do (with the omissions listed above). Where possible, this is achieved by reusing code from Clojure's gvec and ClojureScript's PersistentVector implementations. The Clojure(Script) source files containing the relevant code carry the following copyright notice:

Copyright (c) Rich Hickey. All rights reserved.
The use and distribution terms for this software are covered by the
Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
which can be found in the file epl-v10.html at the root of this distribution.
By using this software in any fashion, you are agreeing to be bound by
  the terms of this license.
You must not remove this notice, or any other, from this software.

Licence

Copyright © 2012-2014 Michał Marczyk, Rich Hickey and contributors

Distributed under the Eclipse Public License 1.0, the same as Clojure. The licence text can be found in the epl-v10.html file at the root of this distribution.

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