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| <title>MADlib: Stemming</title> |
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| <div class="title">Stemming<div class="ingroups"><a class="el" href="group__grp__datatrans.html">Data Types and Transformations</a></div></div> </div> |
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| <div class="contents"> |
| <div class="toc"><b>Contents</b> <ul> |
| <li> |
| <a href="#notes">Implementation Notes</a> </li> |
| <li> |
| <a href="#list">List of Stemmer Operations</a> </li> |
| <li> |
| <a href="#examples">Examples</a> </li> |
| <li> |
| <a href="#related">Related Topics</a> </li> |
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| </div><p>This module provides a basic stemming operation for text input. It is a support module for several machine learning algorithms that require a stemmer. Currently, it only supports English words.</p> |
| <p>This function is a SQL interface to the implementation of the <a href="http://tartarus.org/~martin/PorterStemmer/">Porter Stemming Algorithm</a>. The original stemming algorithm is written and maintained by Martin Porter</p> |
| <p><a class="anchor" id="notes"></a></p><dl class="section user"><dt>Implementation Notes</dt><dd></dd></dl> |
| <p>All functions described in this module work with text OR text array.</p> |
| <p>Several of the function require TEXT VALUES, and returns NULL for a NULL input. See details in description of individual functions.</p> |
| <p><a class="anchor" id="list"></a></p><dl class="section user"><dt>Stemmer Operations</dt><dd><table class="output"> |
| <tr> |
| <th><a class="el" href="porter__stemmer_8sql__in.html#aca5bc24a9a8f5c33470b9f0bf0b3c515" title="Returns stem of input token. Returns NULL if input token is NULL. ">stem_token()</a></th><td><p class="starttd">Returns the stem of the token. Returns NULL if input is NULL.</p> |
| <p class="endtd"></p> |
| </td></tr> |
| <tr> |
| <th><a class="el" href="porter__stemmer_8sql__in.html#a1ac3a2fd645ddf807b36a1328134a4ea" title="Returns stems in an array of input token array. Returns NULL element for corresponding input NULL tok...">stem_token_arr()</a></th><td><p class="starttd">Returns the stems in an array of input token array. The stem would be NULL for corresponding NULL token.</p> |
| <p class="endtd"><a class="anchor" id="examples"></a></p> |
| </td></tr> |
| </table> |
| </dd></dl> |
| <dl class="section user"><dt>Examples</dt><dd></dd></dl> |
| <ol type="1"> |
| <li>Create a table with some words to be stemmed. <pre class="example"> |
| CREATE TABLE token_tbl ( id integer, |
| word text |
| ); |
| INSERT INTO token_tbl VALUES |
| (1, 'kneel'), |
| (2, 'kneeled'), |
| (3, 'kneeling'), |
| (4, 'kneels'), |
| (5, 'knees'), |
| (6, 'knell'), |
| (7, 'knelt'), |
| (8, 'knew'), |
| (9, 'knick'), |
| (10, 'knif'), |
| (11, 'knife'), |
| (12, 'knight'), |
| (13, 'knightly'), |
| (14, 'knights'), |
| (15, 'knit'), |
| (16, 'knits'), |
| (17, 'knitted'), |
| (18, 'knitting'), |
| (19, 'knives'), |
| (20, 'knob'), |
| (21, 'knobs'), |
| (22, 'knock'), |
| (23, 'knocked'), |
| (24, 'knocker'), |
| (25, 'knockers'), |
| (26, 'knocking'), |
| (27, 'knocks'), |
| (28, 'knopp'), |
| (29, 'knot'), |
| (30, 'knots'); |
| </pre></li> |
| <li>Return the stem words <pre class="example"> |
| SELECT madlib.stem_token(word) FROM token_tbl; |
| </pre> <pre class="result"> |
| stem_token |
|  ------------ |
| kneel |
| kneel |
| kneel |
| kneel |
| knee |
| knell |
| knelt |
| knew |
| knick |
| knif |
| knife |
| knight |
| knight |
| knight |
| knit |
| knit |
| knit |
| knit |
| knive |
| knob |
| knob |
| knock |
| knock |
| knocker |
| knocker |
| knock |
| knock |
| knopp |
| knot |
| knot |
| (30 rows) |
| </pre></li> |
| <li>The input can be processed as an array <pre class="example"> |
| SELECT madlib.stem_token_arr(array_agg(word order by word)) FROM token_tbl; |
| </pre> <pre class="result"> |
| stem_token_arr |
|  ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| {kneel,kneel,kneel,kneel,knee,knell,knelt,knew,knick,knif,knife,knight,knight,knight,knit,knit,knit,knit,knive,knob,knob,knock,knock,knocker,knocker,knock,knock,knopp,knot,knot} |
| (1 row) |
| </pre></li> |
| </ol> |
| <p><a class="anchor" id="related"></a></p><dl class="section user"><dt>Related Topics</dt><dd></dd></dl> |
| <p>File <a class="el" href="porter__stemmer_8sql__in.html" title="implementation of porter stemmer operations in SQL ">porter_stemmer.sql_in</a> for list of functions and usage. </p> |
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