问题
What is the easiest way to highlight the difference between two strings in PHP?
I\'m thinking along the lines of the Stack Overflow edit history page, where new text is in green and removed text is in red. If there are any pre-written functions or classes available, that would be ideal.
回答1:
You can use the PHP Horde_Text_Diff package. It suits your needs, and is quite customisable as well.
It's also licensed under the GPL, so Enjoy!
回答2:
Just wrote a class to compute smallest (not to be taken literally) number of edits to transform one string into another string:
http://www.raymondhill.net/finediff/
It has a static function to render a HTML version of the diff.
It's a first version, and likely to be improved, but it works just fine as of now, so I am throwing it out there in case someone needs to generate a compact diff efficiently, like I needed.
Edit: It's on Github now: https://github.com/gorhill/PHP-FineDiff
回答3:
If you want a robust library, Text_Diff (a PEAR package) looks to be pretty good. It has some pretty cool features.
回答4:
This is a nice one, also http://paulbutler.org/archives/a-simple-diff-algorithm-in-php/
Solving the problem is not as simple as it seems, and the problem bothered me for about a year before I figured it out. I managed to write my algorithm in PHP, in 18 lines of code. It is not the most efficient way to do a diff, but it is probably the easiest to understand.
It works by finding the longest sequence of words common to both strings, and recursively finding the longest sequences of the remainders of the string until the substrings have no words in common. At this point it adds the remaining new words as an insertion and the remaining old words as a deletion.
You can download the source here: PHP SimpleDiff...
回答5:
Here is a short function you can use to diff two arrays. It implements the LCS algorithm:
function computeDiff($from, $to)
{
$diffValues = array();
$diffMask = array();
$dm = array();
$n1 = count($from);
$n2 = count($to);
for ($j = -1; $j < $n2; $j++) $dm[-1][$j] = 0;
for ($i = -1; $i < $n1; $i++) $dm[$i][-1] = 0;
for ($i = 0; $i < $n1; $i++)
{
for ($j = 0; $j < $n2; $j++)
{
if ($from[$i] == $to[$j])
{
$ad = $dm[$i - 1][$j - 1];
$dm[$i][$j] = $ad + 1;
}
else
{
$a1 = $dm[$i - 1][$j];
$a2 = $dm[$i][$j - 1];
$dm[$i][$j] = max($a1, $a2);
}
}
}
$i = $n1 - 1;
$j = $n2 - 1;
while (($i > -1) || ($j > -1))
{
if ($j > -1)
{
if ($dm[$i][$j - 1] == $dm[$i][$j])
{
$diffValues[] = $to[$j];
$diffMask[] = 1;
$j--;
continue;
}
}
if ($i > -1)
{
if ($dm[$i - 1][$j] == $dm[$i][$j])
{
$diffValues[] = $from[$i];
$diffMask[] = -1;
$i--;
continue;
}
}
{
$diffValues[] = $from[$i];
$diffMask[] = 0;
$i--;
$j--;
}
}
$diffValues = array_reverse($diffValues);
$diffMask = array_reverse($diffMask);
return array('values' => $diffValues, 'mask' => $diffMask);
}
It generates two arrays:
- values array: a list of elements as they appear in the diff.
- mask array: contains numbers. 0: unchanged, -1: removed, 1: added.
If you populate an array with characters, it can be used to compute inline difference. Now just a single step to highlight the differences:
function diffline($line1, $line2)
{
$diff = computeDiff(str_split($line1), str_split($line2));
$diffval = $diff['values'];
$diffmask = $diff['mask'];
$n = count($diffval);
$pmc = 0;
$result = '';
for ($i = 0; $i < $n; $i++)
{
$mc = $diffmask[$i];
if ($mc != $pmc)
{
switch ($pmc)
{
case -1: $result .= '</del>'; break;
case 1: $result .= '</ins>'; break;
}
switch ($mc)
{
case -1: $result .= '<del>'; break;
case 1: $result .= '<ins>'; break;
}
}
$result .= $diffval[$i];
$pmc = $mc;
}
switch ($pmc)
{
case -1: $result .= '</del>'; break;
case 1: $result .= '</ins>'; break;
}
return $result;
}
Eg.:
echo diffline('StackOverflow', 'ServerFault')
Will output:
S<del>tackO</del><ins>er</ins>ver<del>f</del><ins>Fau</ins>l<del>ow</del><ins>t</ins>
StackOerverfFaulowt
Additional notes:
- The diff matrix requires (m+1)*(n+1) elements. So you can run into out of memory errors if you try to diff long sequences. In this case diff larger chunks (eg. lines) first, then diff their contents in a second pass.
- The algorithm can be improved if you trim the matching elements from the beginning and the end, then run the algorithm on the differing middle only. A latter (more bloated) version contains these modifications too.
回答6:
There is also a PECL extension for xdiff:
- http://php.net/manual/en/book.xdiff.php
- http://pecl.php.net/package/xdiff
In particular:
- xdiff_string_diff — Make unified diff of two strings
Example from PHP Manual:
<?php
$old_article = file_get_contents('./old_article.txt');
$new_article = $_POST['article'];
$diff = xdiff_string_diff($old_article, $new_article, 1);
if (is_string($diff)) {
echo "Differences between two articles:\n";
echo $diff;
}
回答7:
I had terrible trouble with the both the PEAR-based and the simpler alternatives shown. So here's a solution that leverages the Unix diff command (obviously, you have to be on a Unix system or have a working Windows diff command for it to work). Choose your favourite temporary directory, and change the exceptions to return codes if you prefer.
/**
* @brief Find the difference between two strings, lines assumed to be separated by "\n|
* @param $new string The new string
* @param $old string The old string
* @return string Human-readable output as produced by the Unix diff command,
* or "No changes" if the strings are the same.
* @throws Exception
*/
public static function diff($new, $old) {
$tempdir = '/var/somewhere/tmp'; // Your favourite temporary directory
$oldfile = tempnam($tempdir,'OLD');
$newfile = tempnam($tempdir,'NEW');
if (!@file_put_contents($oldfile,$old)) {
throw new Exception('diff failed to write temporary file: ' .
print_r(error_get_last(),true));
}
if (!@file_put_contents($newfile,$new)) {
throw new Exception('diff failed to write temporary file: ' .
print_r(error_get_last(),true));
}
$answer = array();
$cmd = "diff $newfile $oldfile";
exec($cmd, $answer, $retcode);
unlink($newfile);
unlink($oldfile);
if ($retcode != 1) {
throw new Exception('diff failed with return code ' . $retcode);
}
if (empty($answer)) {
return 'No changes';
} else {
return implode("\n", $answer);
}
}
回答8:
This is the best one I've found.
http://code.stephenmorley.org/php/diff-implementation/
回答9:
What you are looking for is a "diff algorithm". A quick google search led me to this solution. I did not test it, but maybe it will do what you need.
回答10:
A php port of Neil Frasers diff_match_patch (Apache 2.0 licensed)
回答11:
I would recommend looking at these awesome functions from PHP core:
similar_text — Calculate the similarity between two strings
http://www.php.net/manual/en/function.similar-text.php
levenshtein — Calculate Levenshtein distance between two strings
http://www.php.net/manual/en/function.levenshtein.php
soundex — Calculate the soundex key of a string
http://www.php.net/manual/en/function.soundex.php
metaphone — Calculate the metaphone key of a string
http://www.php.net/manual/en/function.metaphone.php
回答12:
I came across this PHP diff class by Chris Boulton based on Python difflib which could be a good solution:
PHP Diff Lib
来源：https://stackoverflow.com/questions/321294/highlight-the-difference-between-two-strings-in-php