How to highlight changes/difference in one text paragraph from the other?

Question

Is it possible to highlight the modifications in one text paragraph from the other?

For example, there are 3 text fields in a database. Non-admin users can edit the text

Answer 1

This is an old thread but thought I'd catalog my findings.

If you want to use raw php, this is by far the simplest, fastest, and most effective solution I've found: http://paulbutler.org/archives/a-simple-diff-algorithm-in-php/

From what I can tell, the author of the above code is using an algorithm outlined in this article: http://www.codeproject.com/Articles/6943/A-Generic-Reusable-Diff-Algorithm-in-C-II

Basic description of what's happening (taken from the article):

• Find the current Longest Matching Sequence (LMS) of items.
• Store this LMS in a results pile.
• Process all data left above the LMS using recursion.
• Process all data left below the LMS using recursion.

Works like a charm!

Answer 2

Options:

• PHP Inline Diff (uses PEAR text-diff)
• PEAR Text_Diff
• Diff in Pure PHP
• xdiff_string_diff()

Stackoverflow Archive:

• Highlight the difference between two strings in PHP
• Apply Diff in PHP
• Need Help Optimizing php string difference function

Answer 3

Not sure, why these long solutions are there. here I had found an easy one for me.

string1 = "The quick brown fox jumps over the lazy dog.";
$string2 = "The quick brown albino fox jumps the groovy dog.";

$string1 = explode(" ", $string1);
$string2 = explode(" ", $string2);

$diff = array_intersect($string2, $string1);

$tmp = array();
foreach ($string2 as $k => $w) {
         if ($diff[$k]==$w) {
             $tmp[$k] = $w;
         }
         else {
               $tmp[$k] = "<b>$w</b>";
         }
}
$diff = array_diff($string1, $tmp);

foreach ($diff as $k => $w) {
         $tmp[$k] .= " [<strike>$w</strike>]";
}

echo join (' ', $tmp);

ref. https://forums.phpfreaks.com/topic/6525-how-do-i-highlight-differences-between-strings/

Answer 4

If you are familiar with GNU/Linux tools, you might be familiar with the `diff' tool.

And someone has written a fully functional diff for comparing files/strings in php.

You can find it here: php diff example.