1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
|
<html>
<head>
<title>priority-map - clojure-contrib v1.3 API documentation</title>
<link href="../static/favicon.png" rel="icon" />
<link href="../static/favicon.png" rel="shortcut icon" />
<link media="all" type="text/css" href="../static/clojure.css" rel="stylesheet" />
<link media="all" type="text/css" href="../static/wiki.css" rel="stylesheet" />
<link media="all" type="text/css" href="../static/internal.css" rel="stylesheet" />
<!-- TODO: are we using these (from clojure.org)? If so, add the files -->
<script src="file/view/code_highlighter.js" type="text/javascript"></script>
<script src="file/view/clojure.js" type="text/javascript"></script>
<style>.menuWrapper{height: 36px;}</style>
<!--[if lte IE 6]>
<link rel="stylesheet" href="http://www.wikispaces.com/_/2009051601/s/internal_ie.css" type="text/css" />
<![endif]-->
</head>
<!--
This document was auto-generated from the source by the clojure autodoc system.
To report errors or ask questions about the overall documentation structure, formatting,
etc., contact Tom Faulhaber (google mail name: tomfaulhaber).
For errors in the documentation of a particular namespace, contact the author of that
namespace.
-->
<body>
<div id="AllContentContainer">
<div id="Header">
<a id="Logo" href="index.html"><img alt="Clojure" height="100" width="100" src="../static/clojure-icon.gif" /></a>
<h1><a title="page header title" id="page-header" href="index.html">Clojure-contrib API Reference</a></h1>
</div>
<div id="leftcolumn"><div style="text-align: center;"></div>
<div class="menu">
<div class="WikiCustomNav WikiElement wiki">
<span class="toc-header"><span id="project-name">clojure-contrib</span> <span id="version">v1.3</span> API</span><br />
<ul>
<li><a class="wiki_link" href="index.html">Overview</a></li>
<li><a class="wiki_link" href="api-index.html">API Index</a></li>
</ul>
<span class="toc-header">Namespaces</span>
<ul id="left-sidebar-list">
<li><a href="accumulators-api.html" class="wiki_link">accumulators</a></li><li><a href="agent-utils-api.html" class="wiki_link">agent-utils</a></li><li><a href="base64-api.html" class="wiki_link">base64</a></li><li><a href="classpath-api.html" class="wiki_link">classpath</a></li><li><a href="combinatorics-api.html" class="wiki_link">combinatorics</a></li><li><a href="command-line-api.html" class="wiki_link">command-line</a></li><li><a href="complex-numbers-api.html" class="wiki_link">complex-numbers</a></li><li><a href="cond-api.html" class="wiki_link">cond</a></li><li><a href="condition-api.html" class="wiki_link">condition</a></li><li><a href="core-api.html" class="wiki_link">core</a></li><li><a href="dataflow-api.html" class="wiki_link">dataflow</a></li><li><a href="datalog-api.html" class="wiki_link">datalog</a></li><li><a href="def-api.html" class="wiki_link">def</a></li><li><a href="error-kit-api.html" class="wiki_link">error-kit</a></li><li><a href="except-api.html" class="wiki_link">except</a></li><li><a href="fcase-api.html" class="wiki_link">fcase</a></li><li><a href="find-namespaces-api.html" class="wiki_link">find-namespaces</a></li><li><a href="fnmap-api.html" class="wiki_link">fnmap</a></li><li><a href="gen-html-docs-api.html" class="wiki_link">gen-html-docs</a></li><li><a href="generic.arithmetic-api.html" class="wiki_link">generic.arithmetic</a></li><li><a href="generic.collection-api.html" class="wiki_link">generic.collection</a></li><li><a href="generic.comparison-api.html" class="wiki_link">generic.comparison</a></li><li><a href="generic.functor-api.html" class="wiki_link">generic.functor</a></li><li><a href="generic.math-functions-api.html" class="wiki_link">generic.math-functions</a></li><li><a href="graph-api.html" class="wiki_link">graph</a></li><li><a href="greatest-least-api.html" class="wiki_link">greatest-least</a></li><li><a href="import-static-api.html" class="wiki_link">import-static</a></li><li><a href="jar-api.html" class="wiki_link">jar</a></li><li><a href="java-utils-api.html" class="wiki_link">java-utils</a></li><li><a href="jmx-api.html" class="wiki_link">jmx</a></li><li><a href="json-api.html" class="wiki_link">json</a></li><li><a href="lazy-seqs-api.html" class="wiki_link">lazy-seqs</a></li><li><a href="lazy-xml-api.html" class="wiki_link">lazy-xml</a></li><li><a href="logging-api.html" class="wiki_link">logging</a></li><li><a href="macro-utils-api.html" class="wiki_link">macro-utils</a></li><li><a href="macros-api.html" class="wiki_link">macros</a></li><li><a href="map-utils-api.html" class="wiki_link">map-utils</a></li><li><a href="math-api.html" class="wiki_link">math</a></li><li><a href="miglayout-api.html" class="wiki_link">miglayout</a></li><li><a href="mmap-api.html" class="wiki_link">mmap</a></li><li><a href="mock-api.html" class="wiki_link">mock</a></li><li><a href="monadic-io-streams-api.html" class="wiki_link">monadic-io-streams</a></li><li><a href="monads-api.html" class="wiki_link">monads</a></li><li><a href="ns-utils-api.html" class="wiki_link">ns-utils</a></li><li><a href="priority-map-api.html" class="wiki_link">priority-map</a></li><li><a href="probabilities.finite-distributions-api.html" class="wiki_link">probabilities.finite-distributions</a></li><li><a href="probabilities.monte-carlo-api.html" class="wiki_link">probabilities.monte-carlo</a></li><li><a href="probabilities.random-numbers-api.html" class="wiki_link">probabilities.random-numbers</a></li><li><a href="profile-api.html" class="wiki_link">profile</a></li><li><a href="prxml-api.html" class="wiki_link">prxml</a></li><li><a href="reflect-api.html" class="wiki_link">reflect</a></li><li><a href="repl-ln-api.html" class="wiki_link">repl-ln</a></li><li><a href="repl-utils-api.html" class="wiki_link">repl-utils</a></li><li><a href="seq-api.html" class="wiki_link">seq</a></li><li><a href="server-socket-api.html" class="wiki_link">server-socket</a></li><li><a href="set-api.html" class="wiki_link">set</a></li><li><a href="singleton-api.html" class="wiki_link">singleton</a></li><li><a href="sql-api.html" class="wiki_link">sql</a></li><li><a href="stream-utils-api.html" class="wiki_link">stream-utils</a></li><li><a href="strint-api.html" class="wiki_link">strint</a></li><li><a href="swing-utils-api.html" class="wiki_link">swing-utils</a></li><li><a href="test-base64-api.html" class="wiki_link">test-base64</a></li><li><a href="trace-api.html" class="wiki_link">trace</a></li><li><a href="types-api.html" class="wiki_link">types</a></li><li><a href="with-ns-api.html" class="wiki_link">with-ns</a></li><li><a href="zip-filter-api.html" class="wiki_link">zip-filter</a></li>
</ul>
<div class="BranchTOC">
<span class="toc-header">Other Versions</span>
<ul id="left-sidebar-branch-list">
<li><a href="../index.html" class="wiki_link">v1.2 (stable)</a></li><li><a href="../branch-1.1.x/index.html" class="wiki_link">v1.1 (stable)</a></li>
</ul>
</div>
<a href="http://clojure.org" class="wiki_link">Clojure Home</a>
</div>
</div>
</div>
<div id="rightcolumn">
<div id="Content">
<div class="contentBox"><div class="innerContentBox">
<div id="content_view" class="wiki wikiPage">
<div id="right-sidebar"><div id="toc">
<h1 class="nopad">Table of Contents</h1>
<div style="margin-left: 1em;" class="toc-section">
<a href="#toc0">Overview</a>
<div style="margin-left: 1em;" class="toc-entry">
<a href="#clojure.contrib.priority-map/priority-map">priority-map</a>
</div><div style="margin-left: 1em;" class="toc-entry">
<a href="#clojure.contrib.priority-map/priority-map-by">priority-map-by</a>
</div>
<br />
</div>
</div>
</div>
<div id="content-tag"><h1 id="overview">API for <span id="namespace-name">priority-map</span>
- <span id="header-project">clojure-contrib</span> <span id="header-version">v1.3</span> (<span id="header-status">in development</span>)
</h1>
<span id="author-line">by <span id="author-name">Mark Engelberg</span><br /></span>
<br />Full namespace name: <span id="long-name">clojure.contrib.priority-map</span>
<p></p>
<h2>Overview</h2>
<pre id="namespace-docstr">A priority map is very similar to a sorted map, but whereas a sorted map produces a
sequence of the entries sorted by key, a priority map produces the entries sorted by value.
In addition to supporting all the functions a sorted map supports, a priority map
can also be thought of as a queue of [item priority] pairs. To support usage as
a versatile priority queue, priority maps also support conj/peek/pop operations.
The standard way to construct a priority map is with priority-map:
user=> (def p (priority-map :a 2 :b 1 :c 3 :d 5 :e 4 :f 3))
#'user/p
user=> p
{:b 1, :a 2, :c 3, :f 3, :e 4, :d 5}
So :b has priority 1, :a has priority 2, and so on.
Notice how the priority map prints in an order sorted by its priorities (i.e., the map's values)
We can use assoc to assign a priority to a new item:
user=> (assoc p :g 1)
{:b 1, :g 1, :a 2, :c 3, :f 3, :e 4, :d 5}
or to assign a new priority to an extant item:
user=> (assoc p :c 4)
{:b 1, :a 2, :f 3, :c 4, :e 4, :d 5}
We can remove an item from the priority map:
user=> (dissoc p :e)
{:b 1, :a 2, :c 3, :f 3, :d 5}
An alternative way to add to the priority map is to conj a [item priority] pair:
user=> (conj p [:g 0])
{:g 0, :b 1, :a 2, :c 3, :f 3, :e 4, :d 5}
or use into:
user=> (into p [[:g 0] [:h 1] [:i 2]])
{:g 0, :b 1, :h 1, :a 2, :i 2, :c 3, :f 3, :e 4, :d 5}
Priority maps are countable:
user=> (count p)
6
Like other maps, equivalence is based not on type, but on contents.
In other words, just as a sorted-map can be equal to a hash-map,
so can a priority-map.
user=> (= p {:b 1, :a 2, :c 3, :f 3, :e 4, :d 5})
true
You can test them for emptiness:
user=> (empty? (priority-map))
true
user=> (empty? p)
false
You can test whether an item is in the priority map:
user=> (contains? p :a)
true
user=> (contains? p :g)
false
It is easy to look up the priority of a given item, using any of the standard map mechanisms:
user=> (get p :a)
2
user=> (get p :g 10)
10
user=> (p :a)
2
user=> (:a p)
2
Priority maps derive much of their utility by providing priority-based seq.
Note that no guarantees are made about the order in which items of the same priority appear.
user=> (seq p)
([:b 1] [:a 2] [:c 3] [:f 3] [:e 4] [:d 5])
Because no guarantees are made about the order of same-priority items, note that
rseq might not be an exact reverse of the seq. It is only guaranteed to be in
descending order.
user=> (rseq p)
([:d 5] [:e 4] [:c 3] [:f 3] [:a 2] [:b 1])
This means first/rest/next/for/map/etc. all operate in priority order.
user=> (first p)
[:b 1]
user=> (rest p)
([:a 2] [:c 3] [:f 3] [:e 4] [:d 5])
Priority maps support metadata:
user=> (meta (with-meta p {:extra :info}))
{:extra :info}
But perhaps most importantly, priority maps can also function as priority queues.
peek, like first, gives you the first [item priority] pair in the collection.
pop removes the first [item priority] from the collection.
(Note that unlike rest, which returns a seq, pop returns a priority map).
user=> (peek p)
[:b 1]
user=> (pop p)
{:a 2, :c 3, :f 3, :e 4, :d 5}
It is also possible to use a custom comparator:
user=> (priority-map-by (comparator >) :a 1 :b 2 :c 3)
{:c 3, :b 2, :a 1}
All of these operations are efficient. Generally speaking, most operations
are O(log n) where n is the number of distinct priorities. Some operations
(for example, straightforward lookup of an item's priority, or testing
whether a given item is in the priority map) are as efficient
as Clojure's built-in map.
The key to this efficiency is that internally, not only does the priority map store
an ordinary hash map of items to priority, but it also stores a sorted map that
maps priorities to sets of items with that priority.
A typical textbook priority queue data structure supports at the ability to add
a [item priority] pair to the queue, and to pop/peek the next [item priority] pair.
But many real-world applications of priority queues require more features, such
as the ability to test whether something is already in the queue, or to reassign
a priority. For example, a standard formulation of Dijkstra's algorithm requires the
ability to reduce the priority number associated with a given item. Once you
throw persistence into the mix with the desire to adjust priorities, the traditional
structures just don't work that well.
This particular blend of Clojure's built-in hash sets, hash maps, and sorted maps
proved to be a great way to implement an especially flexible persistent priority queue.
Connoisseurs of algorithms will note that this structure's peek operation is not O(1) as
it would be if based upon a heap data structure, but I feel this is a small concession for
the blend of persistence, priority reassignment, and priority-sorted seq, which can be
quite expensive to achieve with a heap (I did actually try this for comparison). Furthermore,
this peek's logarithmic behavior is quite good (on my computer I can do a million
peeks at a priority map with a million items in 750ms). Also, consider that peek and pop
usually follow one another, and even with a heap, pop is logarithmic. So the net combination
of peek and pop is not much different between this versatile formulation of a priority map and
a more limited heap-based one. In a nutshell, peek, although not O(1), is unlikely to be the
bottleneck in your program.
All in all, I hope you will find priority maps to be an easy-to-use and useful addition
to Clojure's assortment of built-in maps (hash-map and sorted-map).</pre>
<br />
<h2>Public Variables and Functions</h2>
<div id="var-entry">
<br />
<hr />
<h2 id="clojure.contrib.priority-map/priority-map">priority-map</h2>
<span id="var-type">function</span><br />
<pre id="var-usage">Usage: (priority-map & keyvals)
</pre>
<pre id="var-docstr">keyval => key val
Returns a new priority map with supplied mappings</pre>
<a href="http://github.com/clojure/clojure-contrib/blob/37fba7ef6697b2e46db7d38b463dba81d3b1c4e7/modules/priority-map/src/main/clojure/clojure/contrib/priority_map.clj#L306" id="var-source">Source</a>
</div><div id="var-entry">
<br />
<hr />
<h2 id="clojure.contrib.priority-map/priority-map-by">priority-map-by</h2>
<span id="var-type">function</span><br />
<pre id="var-usage">Usage: (priority-map-by comparator & keyvals)
</pre>
<pre id="var-docstr">keyval => key val
Returns a new priority map with supplied mappings</pre>
<a href="http://github.com/clojure/clojure-contrib/blob/37fba7ef6697b2e46db7d38b463dba81d3b1c4e7/modules/priority-map/src/main/clojure/clojure/contrib/priority_map.clj#L312" id="var-source">Source</a>
</div>
</div>
</div>
</div>
</div>
</div>
<div id="foot">
<div style="text-align: center;" id="copyright">Copyright 2007-2010 by Rich Hickey and the various contributors</div>
</div>
</div>
<div id="DesignedBy">Logo & site design by <a title="Visit Tom Hickey's website." href="http://www.tomhickey.com">Tom Hickey</a>.<br />
Clojure auto-documentation system by Tom Faulhaber.</div>
</div>
<!-- /AllContentContainer -->
</body>
</html>
|
