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<title>[GlotPress][881] trunk/gp-includes/strings.php: String functions: introduce a couple of functions to measure string similiarity.</title>
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<div id="msg">
<dl class="meta">
<dt>Revision</dt> <dd><a href="https://glotpress.trac.wordpress.org/changeset/881">881</a></dd>
<dt>Author</dt> <dd>yoavf</dd>
<dt>Date</dt> <dd>2014-04-29 09:41:19 +0000 (Tue, 29 Apr 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>String functions: introduce a couple of functions to measure string similiarity.
gp_levenshtein() lets us compare strings longer than 255 bytes (php native levenshtein limit).
gp_string_similarity() is a wrapper arounds it that returns a score between 0 (no similiarty) and 1 (same string), and makes sure we're not running comparisons on strings longer than 5000 chars (arbirary limit for performance purposes)
See <a href="http://glotpress.trac.wordpress.org/ticket/263">#263</a></pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkgpincludesstringsphp">trunk/gp-includes/strings.php</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="trunkgpincludesstringsphp"></a>
<div class="modfile"><h4>Modified: trunk/gp-includes/strings.php (880 => 881)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/gp-includes/strings.php 2014-04-29 06:47:39 UTC (rev 880)
+++ trunk/gp-includes/strings.php 2014-04-29 09:41:19 UTC (rev 881)
</span><span class="lines">@@ -53,6 +53,16 @@
</span><span class="cx"> }
</span><span class="cx"> endif;
</span><span class="cx">
</span><ins>+if ( function_exists('mb_substr') ):
+ function gp_substr( $haystack, $needle ) {
+ return mb_substr( $haystack, $needle );
+ }
+else:
+ function gp_substr( $haystack, $needle ) {
+ return substr( $haystack, $needle );
+ }
+endif;
+
</ins><span class="cx"> function gp_sanitize_for_url( $name ) {
</span><span class="cx"> $name = trim( $name );
</span><span class="cx"> $name = gp_strtolower( $name );
</span><span class="lines">@@ -73,4 +83,67 @@
</span><span class="cx"> $safe_text = _wp_specialchars( $safe_text, ENT_QUOTES, false, true );
</span><span class="cx"> return apply_filters( 'attribute_escape', $safe_text, $text );
</span><span class="cx">
</span><del>-}
</del><span class="cx">\ No newline at end of file
</span><ins>+}
+
+function gp_string_similarity( $str1, $str2 ) {
+
+ $length1 = gp_strlen( $str1 );
+ $length2 = gp_strlen( $str2 );
+
+ $len = min( $length1, $length2);
+ if ( $len > 5000 ) {
+ //Arbitrary limit on character length for speed purpose.
+ $distance = $len;
+ } else {
+ $distance = gp_levenshtein( $str1, $str2, $length1, $length2 );
+ }
+
+ $similarity = 1 - ( $distance * 0.9 / $len );
+
+ return $similarity;
+}
+
+/*
+ PHP native implementation of levensthein is limited to 255 bytes, so let's extend that
+ Source: https://github.com/wikimedia/mediawiki-extensions-Translate/blob/master/ttmserver/TTMServer.php#L90
+
+*/
+function gp_levenshtein( $str1, $str2, $length1, $length2 ) {
+
+ if ( $length1 == 0 ) {
+ return $length2;
+ }
+
+ if ( $length2 == 0 ) {
+ return $length1;
+ }
+
+ if ( $str1 === $str2 ) {
+ return 0;
+ }
+
+ $bytelength1 = strlen( $str1 );
+ $bytelength2 = strlen( $str2 );
+
+ if ( $bytelength1 === $length1 && $bytelength1 <= 255
+ && $bytelength2 === $length2 && $bytelength2 <= 255 ) {
+ return levenshtein( $str1, $str2 );
+ }
+
+ $prevRow = range( 0, $length2 );
+ for ( $i = 0; $i < $length1; $i++ ) {
+ $currentRow = array();
+ $currentRow[0] = $i + 1;
+ $c1 = gp_substr( $str1, $i, 1 );
+ for ( $j = 0; $j < $length2; $j++ ) {
+ $c2 = gp_substr( $str2, $j, 1 );
+ $insertions = $prevRow[$j + 1] + 1;
+ $deletions = $currentRow[$j] + 1;
+ $substitutions = $prevRow[$j] + ( ( $c1 != $c2 ) ? 1 : 0 );
+ $currentRow[] = min( $insertions, $deletions, $substitutions );
+ }
+ $prevRow = $currentRow;
+ }
+
+ return $prevRow[$length2];
+}
</ins></span></pre>
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