/usr/lib/swi-prolog/doc/Manual/pairs.html

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<h2 id="sec:pairs"><a id="sec:A.18"><span class="sec-nr">A.18</span> <span class="sec-title">library(pairs): 
Operations on key-value lists</span></a></h2>

<p><a id="sec:pairs"></a>

<dl class="tags">
<dt class="tag">author</dt>
<dd>
Jan Wielemaker
</dd>
<dt class="tag">See also</dt>
<dd>
<a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>, <code>library(assoc)</code>
</dd>
</dl>

<p>This module implements common operations on Key-Value lists, also 
known as <i>Pairs</i>. Pairs have great practical value, especially due 
to
<a class="pred" href="builtinlist.html#keysort/2">keysort/2</a> and the 
library <code>assoc.pl</code>.

<p>This library is based on disussion in the SWI-Prolog mailinglist, 
including specifications from Quintus and a library proposal by Richard 
O'Keefe.

<dl class="latex">
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pairs_keys_values/3"><strong>pairs_keys_values</strong>(<var>?Pairs, 
?Keys, ?Values</var>)</a></dt>
<dd class="defbody">
True if <var>Keys</var> holds the keys of <var>Pairs</var> and <var>Values</var> 
the values.

<p>Deterministic if any argument is instantiated to a finite list and 
the others are either free or finite lists. All three lists are in the 
same order.

<dl class="tags">
<dt class="tag">See also</dt>
<dd>
<a class="pred" href="pairs.html#pairs_values/2">pairs_values/2</a> and <a class="pred" href="pairs.html#pairs_keys/2">pairs_keys/2</a>.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pairs_values/2"><strong>pairs_values</strong>(<var>+Pairs, 
-Values</var>)</a></dt>
<dd class="defbody">
Remove the keys from a list of Key-Value pairs. Same as
<code>pairs_keys_values(Pairs, _, Values)</code></dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pairs_keys/2"><strong>pairs_keys</strong>(<var>+Pairs, 
-Keys</var>)</a></dt>
<dd class="defbody">
Remove the values from a list of Key-Value pairs. Same as
<code>pairs_keys_values(Pairs, Keys, _)</code></dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="group_pairs_by_key/2"><strong>group_pairs_by_key</strong>(<var>+Pairs, 
-Joined:list(Key-Values)</var>)</a></dt>
<dd class="defbody">
Group values with the same key. <var>Pairs</var> must be a key-sorted 
list. For example:

<pre class="code">
?- group_pairs_by_key([a-2, a-1, b-4], X).

X = [a-[2,1], b-[4]]
</pre>

<table class="arglist">
<tr><td><var>Pairs</var> </td><td><var>Key</var>-Value list, sorted to 
the standard order of terms (as <a class="pred" href="builtinlist.html#keysort/2">keysort/2</a> 
does) </td></tr>
<tr><td><var>Joined</var> </td><td>List of <var>Key</var>-Group, where 
Group is the list of <var>Values</var> associated with <var>Key</var>. </td></tr>
</table>
</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="transpose_pairs/2"><strong>transpose_pairs</strong>(<var>+Pairs, 
-Transposed</var>)</a></dt>
<dd class="defbody">
Swap Key-Value to Value-Key. The resulting list is sorted using
<a class="pred" href="builtinlist.html#keysort/2">keysort/2</a> on the 
new key.</dd>
<dt class="pubdef"><a id="map_list_to_pairs/3"><strong>map_list_to_pairs</strong>(<var>:Function, 
+List, -Keyed</var>)</a></dt>
<dd class="defbody">
Create a Key-Value list by mapping each element of <var>List</var>. For 
example, if we have a list of lists we can create a list of Length-<var>List</var> 
using

<pre class="code">
        map_list_to_pairs(length, ListOfLists, Pairs),
</pre>

<p></dd>
</dl>

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swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / pairs.html
