Comments on: A simple diff algorithm in PHP

By: Jens

Jens — Thu, 31 Dec 2009 12:51:47 +0000

Paul, this is really a good portion of code in a nice way – thanks a lot. Could you please give us a link to the snipped gbruins mailed you? I am very interested in it. You could send it via mail too.
Wish you a happy new year!

By: Tehem

Tehem — Tue, 06 Oct 2009 19:31:48 +0000

Great code, really useful. I was searching for a text diff without having to install PEAR stuff, that’s it. Thanks a LOT ! I’m very grateful.

By: Niraj

Niraj — Sat, 26 Sep 2009 01:06:37 +0000

A beautiful use of recursion to solve the problem of computing diff!!

By: Chris

Chris — Wed, 05 Aug 2009 15:45:35 +0000

Hi Paul,

I was told to manage a website that actually already uses your algorithm.
After redesigning the program logic and database to handle UTF8-data instead of iso latin1, I discover line breaks being displayed in a wrong way.

Is your algorithm UTF8-safe?

regards, Chris

By: Willem

Willem — Sun, 02 Aug 2009 16:12:01 +0000

Great script, thanks!

By: Henry

Henry — Tue, 12 May 2009 18:59:40 +0000

How hard would it be to adapt this to display the strings side by side with differences highlighted, similar to the wikimedia difference engine?

By: Paul Butler

Paul Butler — Sun, 12 Apr 2009 15:09:55 +0000

Yeah, unfortunately WordPress doesn’t work well with code in comments. Thanks for e-mailing the code, I’ll have a look.

By: gbruins

gbruins — Thu, 09 Apr 2009 18:28:26 +0000

oops that didn’t work out so well. I guess Ill try emailing the code to Paul so he can post it if he wants to. Sorry!

By: gbruins

gbruins — Thu, 09 Apr 2009 18:26:08 +0000

Great function Paul! Thought this might help someone out…here is the “diff” function and the presentation code to display the lines that are different, as well as the actual differences in each line highlighted:

(hoping that my code will remain intact here)

$oldValue){
$newKeys = array_keys($new, $oldValue);

foreach($newKeys as $newIndex){
$matrix[$oldIndex][$newIndex] = isset($matrix[$oldIndex - 1][$newIndex - 1]) ?
$matrix[$oldIndex - 1][$newIndex - 1] + 1 : 1;
if($matrix[$oldIndex][$newIndex] > $maxlen){
$maxlen = $matrix[$oldIndex][$newIndex];
$oldMax = $oldIndex + 1 – $maxlen;
$newMax = $newIndex + 1 – $maxlen;
}
}
}

if($maxlen == 0) {
$diffArray = array(array(‘deleted’=>$old, ‘inserted’=>$new));
} else {
$diffArray = array_merge(
diff(array_slice($old, 0, $oldMax), array_slice($new, 0, $newMax)),
array_slice($new, $newMax, $maxlen),
diff(array_slice($old, $oldMax + $maxlen), array_slice($new, $newMax + $maxlen))
);
}
return $diffArray;
}

$diffArray = diff($f2, $f1);
?>

#diffTable {
border-collapse: collapse;
}

#diffTable td {
padding: 1px 5px 1px 10px;
vertical-align: top;
}

td.lineNumber {
border-right: 1px solid #ccc;
}

span.strDiff {
background-color: #B6FF9F;
padding: 0;
margin: 0;
}

$diff) {
if(!is_array($diff)) {
?>

count($diff['inserted']) ? $diff['deleted'] : $diff['inserted'];
foreach($biggest as $diffKey => $diffVal) {
if(isset($diff['deleted'][$diffKey]) &&
isset($diff['inserted'][$diffKey]) &&
trim($diff['deleted'][$diffKey]) == trim($diff['inserted'][$diffKey])) {
$newStr1 = $diff['deleted'][$diffKey];
$newStr2 = $diff['inserted'][$diffKey];
$backgroundStyle = “”;
} else {
//explode the strings so we can highlight the differences between strings
$str1 = explode(” “, $diff['deleted'][$diffKey]);
$str2 = explode(” “, $diff['inserted'][$diffKey]);
$newStr1 = “”;
$newStr2 = “”;

if(count($str1) >= count($str2)) {
foreach($str1 as $strKey => $strVal) {
if(isset($str1[$strKey]) && isset($str2[$strKey])) {
if($str1[$strKey] != $str2[$strKey]) {
$newStr1 .= ‘ ‘.$str1[$strKey].”;
$newStr2 .= ‘ ‘.$str2[$strKey].”;
} else {
$newStr1 .= ‘ ‘.$str1[$strKey];
$newStr2 .= ‘ ‘.$str2[$strKey];
}
} elseif(isset($str1[$strKey]) && !isset($str2[$strKey])) {
$newStr1 .= ‘ ‘.$str1[$strKey];
$newStr2 .= ”;
} else {
$newStr1 .= ”;
$newStr2 .= ‘ ‘.$str2[$strKey];
}
}
} else {
foreach($str2 as $strKey => $strVal) {
if(isset($str2[$strKey]) && isset($str1[$strKey])) {
if($str2[$strKey] != $str1[$strKey]) {
$newStr1 .= ‘ ‘.$str1[$strKey].”;
$newStr2 .= ‘ ‘.$str2[$strKey].”;
} elseif(isset($str2[$strKey]) && !isset($str1[$strKey])) {
$newStr2 .= ‘ ‘.$str2[$strKey];
$newStr1 .= ”;
} else {
$newStr2 .= ”;
$newStr1 .= ‘ ‘.$str1[$strKey];
}
}
}
}
$backgroundStyle = “background-color: #FFCFCF;”;
}
?>

“>

By: kriplozoik

kriplozoik — Sun, 22 Mar 2009 17:17:02 +0000

I was currently looking for something just like that – simple, independent on other libraries, not hundreds of lines of code.

Nice work and (as said above) thanks for releasing it.