join
Once again, some testing (with thanks to Tiago) showed me that there was still an error in the code. It wasn't coming up with the right distance when a deletion was involved. This is because there was an error in the way that the distance array was instantiated. (Also, my thanks to the editor for making this easier on everyone involved.)
<?php
/*
* This function starts out with several checks in an attempt to save time.
* 1. The shorter string is always used as the "right-hand" string (as the size of the array is based on its length).
* 2. If the left string is empty, the length of the right is returned.
* 3. If the right string is empty, the length of the left is returned.
* 4. If the strings are equal, a zero-distance is returned.
* 5. If the left string is contained within the right string, the difference in length is returned.
* 6. If the right string is contained within the left string, the difference in length is returned.
* If none of the above conditions were met, the Levenshtein algorithm is used.
*/
function LevenshteinDistance($s1, $s2)
{
$nLeftLength = strlen($s1);
$nRightLength = strlen($s2);
if ($nLeftLength >= $nRightLength)
{
$sLeft = $s1;
$sRight = $s2;
} else {
$sLeft = $s2;
$sRight = $s1;
$nLeftLength += $nRightLength; // arithmetic swap of two values
$nRightLength = $nLeftLength - $nRightLength;
$nLeftLength -= $nRightLength;
}
if ($nLeftLength == 0)
return $nRightLength;
else if ($nRightLength == 0)
return $nLeftLength;
else if ($sLeft === $sRight)
return 0;
else if (($nLeftLength < $nRightLength) && (strpos($sRight, $sLeft) !== FALSE))
return $nRightLength - $nLeftLength;
else if (($nRightLength < $nLeftLength) && (strpos($sLeft, $sRight) !== FALSE))
return $nLeftLength - $nRightLength;
else {
$nsDistance = range(0, $nRightLength);
for ($nLeftPos = 1; $nLeftPos <= $nLeftLength; ++$nLeftPos)
{
$cLeft = $sLeft[$nLeftPos - 1];
$nDiagonal = $nLeftPos - 1;
$nsDistance[0] = $nLeftPos;
for ($nRightPos = 1; $nRightPos <= $nRightLength; ++$nRightPos)
{
$cRight = $sRight[$nRightPos - 1];
$nCost = ($cRight == $cLeft) ? 0 : 1;
$nNewDiagonal = $nsDistance[$nRightPos];
$nsDistance[$nRightPos] =
min($nsDistance[$nRightPos] + 1,
$nsDistance[$nRightPos - 1] + 1,
$nDiagonal + $nCost);
$nDiagonal = $nNewDiagonal;
}
}
return $nsDistance[$nRightLength];
}
}
?>
levenshtein
(PHP 4 >= 4.0.1, PHP 5)
levenshtein — Calculate Levenshtein distance between two strings
Description
int levenshtein
( string $str1
, string $str2
[, int $cost_ins
], int $cost_rep
, int $cost_del
)
This function returns the Levenshtein-Distance between the two argument strings or -1, if one of the argument strings is longer than the limit of 255 characters.
The Levenshtein distance is defined as the minimal number of characters you have to replace, insert or delete to transform str1 into str2 . The complexity of the algorithm is O(m*n), where n and m are the length of str1 and str2 (rather good when compared to similar_text(), which is O(max(n,m)**3), but still expensive).
In its simplest form the function will take only the two strings as parameter and will calculate just the number of insert, replace and delete operations needed to transform str1 into str2 .
A second variant will take three additional parameters that define the cost of insert, replace and delete operations. This is more general and adaptive than variant one, but not as efficient.
Example#1 levenshtein() example
<?php
// input misspelled word
$input = 'carrrot';
// array of words to check against
$words = array('apple','pineapple','banana','orange',
'radish','carrot','pea','bean','potato');
// no shortest distance found, yet
$shortest = -1;
// loop through words to find the closest
foreach ($words as $word) {
// calculate the distance between the input word,
// and the current word
$lev = levenshtein($input, $word);
// check for an exact match
if ($lev == 0) {
// closest word is this one (exact match)
$closest = $word;
$shortest = 0;
// break out of the loop; we've found an exact match
break;
}
// if this distance is less than the next found shortest
// distance, OR if a next shortest word has not yet been found
if ($lev <= $shortest || $shortest < 0) {
// set the closest match, and shortest distance
$closest = $word;
$shortest = $lev;
}
}
echo "Input word: $input\n";
if ($shortest == 0) {
echo "Exact match found: $closest\n";
} else {
echo "Did you mean: $closest?\n";
}
?>
上例将输出：
Input word: carrrot Did you mean: carrot?
See also soundex(), similar_text(), and metaphone().
add a note
User Contributed Noteslevenshtein
paulroweatinamedotcom
23-Nov-2008 12:57
23-Nov-2008 12:57
paulrowe at iname dot com
28-Aug-2008 08:58
28-Aug-2008 08:58
[EDITOR'S NOTE: original post and 2 corrections combined into 1 -- mgf]
Here is an implementation of the Levenshtein Distance calculation that only uses a one-dimensional array and doesn't have a limit to the string length. This implementation was inspired by maze generation algorithms that also use only one-dimensional arrays.
I have tested this function with two 532-character strings and it completed in 0.6-0.8 seconds.
<?php
/*
* This function starts out with several checks in an attempt to save time.
* 1. The shorter string is always used as the "right-hand" string (as the size of the array is based on its length).
* 2. If the left string is empty, the length of the right is returned.
* 3. If the right string is empty, the length of the left is returned.
* 4. If the strings are equal, a zero-distance is returned.
* 5. If the left string is contained within the right string, the difference in length is returned.
* 6. If the right string is contained within the left string, the difference in length is returned.
* If none of the above conditions were met, the Levenshtein algorithm is used.
*/
function LevenshteinDistance($s1, $s2)
{
$sLeft = (strlen($s1) > strlen($s2)) ? $s1 : $s2;
$sRight = (strlen($s1) > strlen($s2)) ? $s2 : $s1;
$nLeftLength = strlen($sLeft);
$nRightLength = strlen($sRight);
if ($nLeftLength == 0)
return $nRightLength;
else if ($nRightLength == 0)
return $nLeftLength;
else if ($sLeft === $sRight)
return 0;
else if (($nLeftLength < $nRightLength) && (strpos($sRight, $sLeft) !== FALSE))
return $nRightLength - $nLeftLength;
else if (($nRightLength < $nLeftLength) && (strpos($sLeft, $sRight) !== FALSE))
return $nLeftLength - $nRightLength;
else {
$nsDistance = range(1, $nRightLength + 1);
for ($nLeftPos = 1; $nLeftPos <= $nLeftLength; ++$nLeftPos)
{
$cLeft = $sLeft[$nLeftPos - 1];
$nDiagonal = $nLeftPos - 1;
$nsDistance[0] = $nLeftPos;
for ($nRightPos = 1; $nRightPos <= $nRightLength; ++$nRightPos)
{
$cRight = $sRight[$nRightPos - 1];
$nCost = ($cRight == $cLeft) ? 0 : 1;
$nNewDiagonal = $nsDistance[$nRightPos];
$nsDistance[$nRightPos] =
min($nsDistance[$nRightPos] + 1,
$nsDistance[$nRightPos - 1] + 1,
$nDiagonal + $nCost);
$nDiagonal = $nNewDiagonal;
}
}
return $nsDistance[$nRightLength];
}
}
?>
luka8088 at gmail dot com
29-May-2008 04:03
29-May-2008 04:03
Simple levenshtein function without string length limit ...
<?php
function levenshtein2($str1, $str2, $cost_ins = null, $cost_rep = null, $cost_del = null) {
$d = array_fill(0, strlen($str1) + 1, array_fill(0, strlen($str2) + 1, 0));
$ret = 0;
for ($i = 1; $i < strlen($str1) + 1; $i++)
$d[$i][0] = $i;
for ($j = 1; $j < strlen($str2) + 1; $j++)
$d[0][$j] = $j;
for ($i = 1; $i < strlen($str1) + 1; $i++)
for ($j = 1; $j < strlen($str2) + 1; $j++) {
$c = 1;
if ($str1{$i - 1} == $str2{$j - 1})
$c = 0;
$d[$i][$j] = min($d[$i - 1][$j] + 1, $d[$i][$j - 1] + 1, $d[$i - 1][$j - 1] + $c);
$ret = $d[$i][$j];
}
return $ret;
}
?>
atx dot antrax at gmail dot com
18-Apr-2008 05:42
18-Apr-2008 05:42
I have made a function that removes the length-limit of levenshtein function and ajust the result with similar_text:
<?php
function _similar($str1, $str2) {
$strlen1=strlen($str1);
$strlen2=strlen($str2);
$max=max($strlen1, $strlen2);
$splitSize=250;
if($max>$splitSize)
{
$lev=0;
for($cont=0;$cont<$max;$cont+=$splitSize)
{
if($strlen1<=$cont || $strlen2<=$cont)
{
$lev=$lev/($max/min($strlen1,$strlen2));
break;
}
$lev+=levenshtein(substr($str1,$cont,$splitSize), substr($str2,$cont,$splitSize));
}
}
else
$lev=levenshtein($str1, $str2);
$porcentage= -100*$lev/$max+100;
if($porcentage>75)//Ajustar con similar_text
similar_text($str1,$str2,$porcentage);
return $porcentage;
}
?>
dale3h
13-Feb-2008 12:52
13-Feb-2008 12:52
Using PHP's example along with Patrick's comparison percentage function, I have come up with a function that returns the closest word from an array, and assigns the percentage to a referenced variable:
<?php
function closest_word($input, $words, &$percent = null) {
$shortest = -1;
foreach ($words as $word) {
$lev = levenshtein($input, $word);
if ($lev == 0) {
$closest = $word;
$shortest = 0;
break;
}
if ($lev <= $shortest || $shortest < 0) {
$closest = $word;
$shortest = $lev;
}
}
$percent = 1 - levenshtein($input, $closest) / max(strlen($input), strlen($closest));
return $closest;
}
?>
Usage:
<?php
$input = 'carrrot';
$words = array('apple','pineapple','banana','orange',
'radish','carrot','pea','bean','potato');
$percent = null;
$found = closest_word($input, $words, $percent);
printf('Closest word to "%s": %s (%s%% match)', $input, $found, round($percent * 100, 2));
?>
I found that lowercasing the array prior to comparing yields a better comparison when the case is not of importance, for example: comparing a user-inputted category to a list of existing categories.
I also found that when the percentage was above 75%, it was usually the match that I was looking for.
Patrick Palka
09-Apr-2007 05:47
09-Apr-2007 05:47
To find the comparison percentage of levenshtein, use this function:
<?php
function _levenshtein($str1, $str2) {
return 1-levenshtein($str1, $str2)/max(strlen($str1), strlen($str2));
}
echo _levenshtein('dogs', 'cats'); //.25
This function (along with levenshtein) is obsolete though: similar_text is 20% faster that the two.
?>
Paul
03-Mar-2007 02:47
03-Mar-2007 02:47
@ ivo_gelov at gmx dot net
Your implementation of Myers' algorithm is not entirely correct. The algorithm finds the end of a match, but you still need to find the start of a match. The easiest way to find the start of a match is to execute the algorithm again on the reversed string, starting at the j'th character. You can't just assume the start of the match is at j - m because you don't know whether the match is longer, shorter, or of equal length.
Just my 2 cents.
ivo_gelov at gmx dot net
30-Oct-2006 11:03
30-Oct-2006 11:03
Here is a small function to implement a fuzzy search.
If someone is wondering about the mathematics inside, this information can be found in "A fast bit-vector algorithm for approximate string matching based on dynamic programming" by Gene Myers, May 27 1998
<?php
// This can search for PATTERN into HAYSTACK with MIST mistaken symbols in PATTERN
// OK_MATCH is a function ($Position, $Score)
// Position is zero-based index in HAYSTACK, where PATTERN is found,
// and Score is the number of mistaken symbols
function FuzzyLook($pattern,$haystack,$mist,$ok_match)
{
$m = strlen($pattern);
$n = strlen($haystack);
if($n==0 OR $m==0) return;
// Precompute Peq[Z]
for($i=0; $i<32; $i++) $Bit[$i] = (1 << $i);
for($i=0; $i<$m; $i++) $Peq[ ord(substr($pattern,$i,1)) ] |= $Bit[$i];
$Pv = 0xFFFFFFFF;
$Mv = 0;
$Score = $m;
for($j=0; $j<$n; $j++)
{
$Eq = $Peq[ ord(substr($haystack,$j,1))];
$Xv = $Eq | $Mv;
$Xh = ((($Eq & $Pv) + $Pv) ^ $Pv) | $Eq;
$Ph = $Mv | ~ ($Xh | $Pv);
$Mh = $Pv & $Xh;
if($Ph & (1 << ($m-1))) $Score += 1;
elseif($Mh & (1 << ($m-1))) $Score -= 1;
$Ph <<= 1;
$Pv = ($Mh << 1) | ~ ($Xv | $Ph);
$Mv = $Ph & $Xv;
if($Score <= $mist && $j>=$m-1) $ok_match($j-$m+1,$Score);
}
}
?>
carey at NOSPAM dot internode dot net dot au
28-Oct-2006 10:06
28-Oct-2006 10:06
I have found that levenshtein is actually case-sensitive (in PHP 4.4.2 at least).
<?php
$distance=levenshtein('hello','ELLO');
echo "$distance";
?>
Outputs: "5", instead of "1". If you are implementing a fuzzy search feature that makes use of levenshtein, you will probably need to find a way to work around this.
dinesh AT dinsoft DOT net
18-Mar-2006 07:18
18-Mar-2006 07:18
Here is a string resynch function:
<?php
// Trouve les operations a effectuer pour modifier $b en $a en exploitant leurs similitudes (Finds the operations required to change $b to $a)
// Identique a la fonction Resynch Compare de Hex Workshop
//
// Parametres:
// $a Premiere chaine (cible, target)
// $b Seconde chaine (source)
// $l Nombre d'octets devant correspondre pour etre consides comme un bloc similaire (number of matching bytes required)
// $s Distance maximale dans laquelle les blocs similaires sont cherches (search window)
//
// Retourne:
// Array
// Array
// [0] Operation: + Add , - Del , / Replace, = Match
// [1] Source offset
// [2] Source count
// [3] Target offset
// [4] Target count
//
function str_resynch($a,$b,$l=32,$s=2048) {
$r=array();
for($i=0,$c=strlen($a),$cc=strlen($b),$ii=0,$z=$s-1,$z2=($z<<1)+1; $i<$c; $i++) {
$d=$i-$z;
$d=($d<$ii)?substr($b,$ii,$z2-$ii+$d):substr($b,$d,$z2);
$p=strpos($d,$a{$i});
$n=0;
while ($p!==FALSE) {
$m=1;
$bi=$i;
$bp=$p;
$p+=$ii;
while ((++$i<$c) && (++$p<$cc)) {
if ($a{$i}!=$b{$p}) break;
$m++;
}
if ($m<$l) {
$i=$bi;
$n=$bp+1;
$p=@strpos($d,$a{$i},$n);
}
else {
$i--;
$r[]=array($bi,$bp+$ii,$m); // offset a, offset b, Count
$ii=$p;
break;
}
}
}
if (!count($r)) return ($cc)?array('/',0,$c,0,$cc):array(array('+',0,$c,0,0));
$o=array();
$bi=0;
$bp=0;
for($i=0,$m=count($r);$i<$m;$i++) {
if ($r[$i][0]!=$bi) {
if ($r[$i][1]!=$bp) {
// Replace
$o[]=array('/',$bi,$r[$i][0]-$bi,$bp,$r[$i][1]-$bp);
$bi=$r[$i][0];
$bp=$r[$i][1];
}
else {
// Insertion
$o[]=array('+',$bi,$r[$i][0]-$bi,$bp,0);
$bi=$r[$i][0];
}
}
elseif ($r[$i][1]!=$bp) {
// Delete
$o[]=array('-',$bi,0,$bp,$r[$i][1]-$bp);
$bp=$r[$i][1];
}
// Match
$o[]=array('=',$r[$i][0],$r[$i][2],$r[$i][1],$r[$i][2]);
$bi+=$r[$i][2];
$bp+=$r[$i][2];
}
if ($c!=$bi) {
if ($cc!=$bp) $o[]=array('/',$bi,$c-$bi,$bp,$cc-$bp);
else $o[]=array('+',$bi,$c-$bi,$bp,0);
}
elseif ($cc!=$bp) $o[]=array('-',$bi,0,$bp,$cc-$bp);
return $o;
}
?>
june05 at tilo-hauke dot de
06-Jun-2005 03:44
06-Jun-2005 03:44
//levenshtein for arrays
function array_levenshtein($array1,$array2)
{ $aliases= array_flip(array_values(array_unique(array_merge($array1,$array2))));
if(count($aliases)>255) return -1;
$stringA=''; $stringB='';
foreach($array1 as $entry) $stringA.=chr($aliases[$entry]);
foreach($array2 as $entry) $stringB.=chr($aliases[$entry]);
return levenshtein($stringA,$stringB);
}
// e.g. use array_levenshtein to detect special expressions in unser-inputs
echo array_levenshtein(split(" ", "my name is xxx"), split(" ","my name is levenshtein"));
//output: 1
justin at visunet dot ie
05-Apr-2005 10:46
05-Apr-2005 10:46
<?php
/*********************************************************************
* The below func, btlfsa, (better than levenstien for spelling apps)
* produces better results when comparing words like haert against
* haart and heart.
*
* For example here is the output of levenshtein compared to btlfsa
* when comparing 'haert' to 'herat, haart, heart, harte'
*
* btlfsa('haert','herat'); output is.. 3
* btlfsa('haert','haart'); output is.. 3
* btlfsa('haert','harte'); output is.. 3
* btlfsa('haert','heart'); output is.. 2
*
* levenshtein('haert','herat'); output is.. 2
* levenshtein('haert','haart'); output is.. 1
* levenshtein('haert','harte'); output is.. 2
* levenshtein('haert','heart'); output is.. 2
*
* In other words, if you used levenshtein, 'haart' would be the
* closest match to 'haert'. Where as, btlfsa sees that it should be
* 'heart'
*/
function btlfsa($word1,$word2)
{
$score = 0;
// For each char that is different add 2 to the score
// as this is a BIG difference
$remainder = preg_replace("/[".preg_replace("/[^A-Za-z0-9\']/",' ',$word1)."]/i",'',$word2);
$remainder .= preg_replace("/[".preg_replace("/[^A-Za-z0-9\']/",' ',$word2)."]/i",'',$word1);
$score = strlen($remainder)*2;
// Take the difference in string length and add it to the score
$w1_len = strlen($word1);
$w2_len = strlen($word2);
$score += $w1_len > $w2_len ? $w1_len - $w2_len : $w2_len - $w1_len;
// Calculate how many letters are in different locations
// And add it to the score i.e.
//
// h e a r t
// 1 2 3 4 5
//
// h a e r t a e = 2
// 1 2 3 4 5 1 2 3 4 5
//
$w1 = $w1_len > $w2_len ? $word1 : $word2;
$w2 = $w1_len > $w2_len ? $word2 : $word1;
for($i=0; $i < strlen($w1); $i++)
{
if ( !isset($w2[$i]) || $w1[$i] != $w2[$i] )
{
$score++;
}
}
return $score;
}
// *************************************************************
// Here is a full code example showing the difference
$misspelled = 'haert';
// Imagine that these are sample suggestions thrown back by soundex or metaphone..
$suggestions = array('herat', 'haart', 'heart', 'harte');
// Firstly order an array based on levenshtein
$levenshtein_ordered = array();
foreach ( $suggestions as $suggestion )
{
$levenshtein_ordered[$suggestion] = levenshtein($misspelled,$suggestion);
}
asort($levenshtein_ordered, SORT_NUMERIC );
print "<b>Suggestions as ordered by levenshtein...</b><ul><pre>";
print_r($levenshtein_ordered);
print "</pre></ul>";
// Secondly order an array based on btlfsa
$btlfsa_ordered = array();
foreach ( $suggestions as $suggestion )
{
$btlfsa_ordered[$suggestion] = btlfsa($misspelled,$suggestion);
}
asort($btlfsa_ordered, SORT_NUMERIC );
print "<b>Suggestions as ordered by btlfsa...</b><ul><pre>";
print_r($btlfsa_ordered);
print "</pre></ul>";
?>
mcreuzer at r-world dot com
08-Mar-2005 01:01
08-Mar-2005 01:01
I am using the Levenshtein distance to SORT my search results.
I have a search page for peoples names. I do a SOUNDEX() search on the name in mysql. MySQL SOUNDEX() will perform the "fuzzy" search for me.
I then calculate the Levenshtein distance between the search term and the actual name found by the SOUNDEX() search. This will give me a score on how close my results are to the search string.
I can the sort my results for display listing the closest results first.
<?php
// PHP CODE INCLUDING DB LOOKUPS HERE
usort($searchresults, "finallevenshteinsortfunction");
function finallevenshteinsortfunction($a, $b)
{
if(($a['levenshtein'] > $b['levenshtein']) || ( $a['levenshtein'] == $b['levenshtein'] && strnatcasecmp( $a['Last_Name'], $b['Last_Name']) >= 1) ){ return $a['levenshtein'];} // Ok... The levenstein is greater OR with the same levenshtein, the last name is alphanumerically first
elseif($a['levenshtein'] == $b['levenshtein']){ return '0';} // The levenstein matches
elseif($a['levenshtein'] < $b['levenshtein']){ return -$a['levenshtein'];}
else{die("<!-- a horrable death -->");}
}
?>
brett at webfroot dot co dot nz
17-Nov-2004 02:58
17-Nov-2004 02:58
More information on Levenshtein distances on Wikipedia:
http://en.wikipedia.org/wiki/Levenshtein_distance
elonen at iki dot fi
05-Nov-2004 05:58
05-Nov-2004 05:58
If you need to *search* for approximate matches in a large text mass (sort of like a fuzzy version of strpos), try this:
http://iki.fi/elonen/code/misc-notes/appr-search-php/
silas at silaspalmer dot com
28-Feb-2004 06:52
28-Feb-2004 06:52
Some code for a basic fuzzy search.
<?php
$needle = "Youser Nein stitched tymes hand";
$haystack = "
Did you know that a stitch in time can save nine. Isn't that amazing! I think so
The user-supplied function has to return the loser, from the sand. Describe the cost for this particular operation.
Eweser may decide to use only some of the supplied nans. And pay attention. This isn't hard...
";
// explode into words
$hwords = preg_split("/[\s\W]+/", $haystack);
$nwords = preg_split("/[\s\W]+/", $needle);
echo "You searched for $needle<br>";
echo "I found...<br>";
foreach ($hwords as $hkey => $hayword) {
$hmp = metaphone ($hayword);
foreach ($nwords as $nkey => $needword) {
// First or last letters of needle and haystack have to match (case insensitive)
$nfirst = strtolower(substr($needword, 0, 1));
$nlast = strtolower(substr($needword, -1));
$hfirst = strtolower(substr($hayword, 0, 1));
$hlast = strtolower(substr($hayword, -1));
if (($hfirst == $nfirst) or ($hlast == $nlast)) {
$nmp = metaphone ($needword);
$distance = levenshtein ($hmp, $nmp);
// $distance = levenshtein ($hayword, $needword);
$n_len = strlen($nmp);
$per = round(($distance/$n_len)*1000);
if ($per < 335) {
// Highlight word in haystack
$haystack = str_replace($hayword, "<b>$hayword</b>", $haystack);
$haystack = str_replace("<b><b>", "<b>", $haystack);
$haystack = str_replace("</b></b>", "</b>", $haystack);
}
}
}
}
// echo the new haystack
echo $haystack;
// Returns ...
//
// You searched for Youser Nein stitched tymes hand
// I found...
// Did you know that a <b>stitch</b> in <b>time</b> can
// save <b>nine</b>. Isn't that amazing! I think so. The
// <b>user</b>-supplied function has to return the
// <b>loser</b>, from the sand. Describe the cost for this
// particular operation. Eweser may decide to use only some
// of the supplied nans. <b>And</b> pay attention. This
// isn't <b>hard</b>...
?>
gzink at zinkconsulting dot com
03-Dec-2003 07:03
03-Dec-2003 07:03
Try combining this with metaphone() for a truly amazing fuzzy search function. Play with it a bit, the results can be plain scary (users thinking the computer is almost telepathic) when implemented properly. I wish spell checkers worked as well as the code I've written.
I would release my complete code if reasonable, but it's not, due to copyright issues. I just hope that somebody can learn from this little tip!
genialbrainmachine at dot IHATESPAM dot tiscali dot it
27-Oct-2003 03:55
27-Oct-2003 03:55
I wrote this function to have an "intelligent" comparison between data to be written in a DB
and already existent data. Not ony calculating distances but also balancing distances for
each field.
<?php
/*
This function calculate a balanced percentage distance between an array of strings
"$record" and a compared array "$compared", balanced through an array of
weights "$weight". The three arrays must have the same indices.
For an unbalanced distance, set all weights to 1.
The used formula is:
percentage distance = sum(field_levenshtein_distance * field_weight) / sum(record_field_length * field_weight) * 100
*/
function search_similar($record, $weights, $compared, $precision=2) {
$field_names = array_keys($record);
# "Weighted length" of $record and "weighted distance".
foreach ($field_names as $field_key) {
$record_weight += strlen($record[$field_key]) * $weights[$field_key];
$weighted_distance += levenshtein($record[$field_key],$compared[$field_key]) * $weights[$field_key];
}
# Building the result..
if ($record_weight) {
return round(($weighted_distance / $record_weight * 100),$precision);
} elseif ((strlen(implode("",$record)) == 0) && (strlen(implode("",$compared)) == 0)) { // empty records
return round(0,$precision);
} elseif (array_sum($weights) == 0) { // all weights == 0
return round(0,$precision);
} else {
return false;
}
/*
Be very careful distinguising 0 result and false result.
The function results 0 ('0.00' if $precision is 2 and so on) if:
- $record and $compared are equals (even if $record and $compared are empty);
- all weights are 0 (the meaning could be "no care about any field").
Conversely, the function results false if $record is empty, but the weights
are not all 0 and $compared is not empty. That cause a "division by 0" error.
I wrote this kind of check:
if ($rel_dist = search_similar(...)) {
print $rel_dist;
} elseif ($rel_dist == "0.00") { // supposing that $precision is 2
print $rel_dist;
} else {
print "infinite";
}
*/
}
?>
jlsalinas at gmx dot net
26-Oct-2003 10:28
26-Oct-2003 10:28
Regarding the post by fgilles on April 26th 2001, I suggest not to use levenshtein() function to test for over-uppercasing unless you've got plenty of time to waste in your host. ;) Anyhow, I think it's a useful feature, as I get really annoyed when reading whole messages in uppercase.
PHP's levenshtein() function can only handle up to 255 characters, which is not realistic for user input (only the first paragraph oh this post has 285 characters). If you choose to use a custom function able to handle more than 255 characters, efficiency is an important issue.
I use this function, specific for this case, but much faster:
function ucase_percent ($str) {
$str2 = strtolower ($str);
$l = strlen ($str);
$ucase = 0;
for ($i = 0; $i < $l; $i++) {
if ($str{$i} != $str2{$i}) {
$ucase++;
}
}
return $ucase / $l * 100.0;
}
I think 10% is enough for written English (maybe other languages like German, which use more capital letters, need more). With some sentencies in uppercase (everybody has