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Persistent sorted maps and sets with log-time rank queries
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data.avl

Persistent sorted maps and sets with support for the full clojure.core sorted collections API (in particular clojure.core/(r)?(sub)?seq), transients and additional logarithmic time operations: rank queries (via clojure.core/nth and clojure.data.avl/rank-of), "nearest key" lookups, splits by index or key and subsets/submaps.

Persistent AVL trees are used as the underlying data structure.

Synopsis

data.avl supports both Clojure and ClojureScript. It exports a single namespace with nine public functions, four of which are constructor functions which can be used as drop-in replacements for clojure.core / cljs.core functions of the same names, while the remaining five expose data.avl-specific functionality:

(require '[clojure.data.avl :as avl])

;; drop-in replacements for clojure.core counterparts
(doc avl/sorted-map)
(doc avl/sorted-map-by)
(doc avl/sorted-set)
(doc avl/sorted-set-by)

;; find rank of element as primitive long, -1 if not found
(doc avl/rank-of)

;; find element closest to the given key and </<=/>=/> according
;; to coll's comparator
(doc avl/nearest)

;; split the given collection at the given key returning
;; [left entry? right]
(doc avl/split-key)

;; split the given collection at the given index; similar to
;; clojure.core/split-at, but operates on and returns data.avl
;; collections
(doc avl/split-at)

;; return subset/submap of the given collection; accepts arguments
;; reminiscent of clojure.core/{subseq,rsubseq}
(doc avl/subrange)

All data.avl collection-returning public functions return first-class collections (see below for a discussion).

Description

data.avl maps and sets behave like the core Clojure variants, with the following differences:

  1. They have transient counterparts:

    (persistent! (assoc! (transient (avl/sorted-map) 0 0)))
    ;= {0 0}
    

    and use transients during construction:

    (apply avl/sorted-map (interleave (range 32) (range 32)))
    ;; ^- uses transients
    
  2. They are typically noticeably faster during lookups and somewhat slower during non-transient "updates" (assoc, dissoc) than the built-in sorted collections. Note that batch "updates" using transients typically perform better than batch "updates" on the non-transient-enabled built-ins.

  3. They add some memory overhead -- a reference and two ints per key. The additional node fields are used to support transients (one reference field per key), rank queries (one int) and the rebalancing algorithm itself (the final int).

Additionally, data.avl collections support several features that the built-ins do not:

  1. Logarithmic time rank queries via clojure.core/nth and clojure.data.avl/rank-of:

    (nth (avl/sorted-map 0 0 1 1 2 2) 1)
    ;= [1 1]
    (nth (avl/sorted-set 0 1 2) 1)
    ;= 1
    
    (avl/rank-of (avl/sorted-map-by > 0 0 1 1 2 2) 0)
    2
    (avl/rank-of (avl/sorted-set-by > 0 1 2) 0)
    2
    
  2. Logarithmic time lookups of "nearest entries" via clojure.data.avl/nearest:

    (avl/nearest (avl/sorted-set 0 1 2) < 1)
    ;= 0
    (avl/nearest (avl/sorted-set 0 1 2) <= 1) ; or >=
    ;= 1
    (avl/nearest (avl/sorted-set 0 1 2) > 1)
    ;= 2
    (avl/nearest (avl/sorted-set 0 1 2) > 2)
    ;= nil
    
  3. Logarithmic time splitting by key:

    (avl/split-key 3 (avl/sorted-set 0 1 2 3 4 5))
    ;= [#{0 1 2} 3 #{4 5 6}]
    (avl/split-key 1 (avl/sorted-map 0 0 1 1 2 2))
    ;= [{0 0} [1 1] {2 2}]
    (avl/split-key 2 (avl/sorted-set 0 1 3 4))
    ;= [#{0 1} nil #{3 4}]
    

    The middle element of the returned vector is the entry at the given key for maps, stored copy of the key for sets and nil if the key is absent from the collection.

    The remaining two elements are the "left" and "right" subcollections of the original collection argument when split with the given key, comprising, respectively, the keys preceding and succeeding the given key in the order determined by the input collection's comparator.

  4. Logarithmic time splitting by index:

    (avl/split-at 2 (avl/sorted-set 0 1 2 3 4 5))
    ;= [#{0 1} #{2 3 4 5}]
    
  5. Logarithmic time slicing:

    (avl/subrange (avl/sorted-set 0 1 2 3 4 5) > 1)
    ;= #{2 3 4 5}
    (avl/subrange (avl/sorted-set 0 1 2 3 4 5) <= 4)
    ;= #{0 1 2 3 4}
    (avl/subrange (avl/sorted-set 0 1 2 3 4 5) >= 2 < 5)
    ;= #{2 3 4}
    
  6. clojure.data.avl/split-key, clojure.data.avl/split-at and clojure.data.avl/subrange all return first-class data.avl collections, completely independent of the originals. In particular, they do not prevent the originals from being garbage collected and they support insertion of arbitrary keys, including outside original subrange bounds.

Releases and dependency information

data.avl requires Clojure >= 1.5.0. The ClojureScript version is regularly tested against the most recent ClojureScript release.

data.avl 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/data.avl "${version}"]

Maven dependency information:

<dependency>
  <groupId>org.clojure</groupId>
  <artifactId>data.avl</artifactId>
  <version>${version}</version>
</dependency>

Gradle dependency information:

compile "org.clojure:data.avl:${version}"

Developer information

data.avl 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

data.avl sorted maps and sets support the same basic functionality regular Clojure's sorted maps and sets do (with the additions listed above). Some of the code supporting various Clojure(Script) interfaces and protocols is adapted from the ClojureScript implementations of the red-black-tree-based sorted collections, which themselves are ports of Clojure's implementations written in Java. 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 © 2013-2016 Michał Marczyk, Rich Hickey and contributors

Distributed under the Eclipse Public License, the same as Clojure.

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