highlighting changes in color in a paragraph

OwenTheSamoan

I'm trying to highlight text changes in color in a paragraph. Basically, I am comparing one string of words with another string and I want to change the color of the font in the second string to show what changes have been added. The coding I am using works for the most part, but there are still some errors in it. Certain words are not highlighted completely when they should be and for no apparent reason one particular letter will have the font color changed throughout the string for no reason. Can anybody see where I am going wrong with the supplied text? I gave a comparison of two strings. Thanks in advance.

$old_string = "abc d e f g hafka hhd nn";
$new_string = "abc d e f g new change hafka in string hhd nn";

$old2 = explode(' ', $old_string);
$new2 = explode(' ', $new_string);

// What's different in $new?
$differences = (array_diff($new2, $old2));

foreach($differences as $word)
{
$replacement = "".$word."";
$new_string = str_replace($word, $replacement, ($new_string));
}
echo " ";
echo "$new_string";

gardnc

Look at the old vs new:

old: abc d e f g hafka hhd nn
new: abc d e f g new change hafka in string hhd nn

and I think you'll see the error in your logic.

OwenTheSamoan

In theory the highlighted string should look like this--

abc d e f g new change hafka in string hhd nn

If I substitute
// What's different in $new?
$differences = (array_diff($new2, $old2));

for an array like this, it works perfectly--
$differences = array('new change', 'in string');

gardnc

Owen,

Your logic assumes there will only be one substitution necessary per element and does not take into consideration the context of the found string, i.e. the sting "in" in "string".

OwenTheSamoan

I understand what you are saying. I tried using array_unique() but that didn't help. I see that the problem is in the foreach() loop. Any suggestions on how to remedy this?

gardnc

The problem is not so much the code used, but the overall logic.

You probably need to draw this function out in a flow chart and you'll need several steps of logic to arrive at your solution. I would suggest searching for book on the subject. Also, there may be a class already developed by someone for this purpose - try phpclasses.org (I understand if you don't use Firefox with adblock the site can be very annoying); three classes I located:

Class: File Diff (diff) - PHP Classes
This class can locate the differences between two given text files It can also
display the lines that are different in an HTML table highlighting the ...
www.phpclasses.org/browse/package/2302.html - Similar pages

Classes: Text processing - PHP Classes
Manipulating and validating text data. ... Search for text in files like the Unix grep tool ...... Compare and extract differences between texts ...
www.phpclasses.org/browse/class/25.html - Similar pages

Class: Compare Files (compare) - PHP Classes
This class can compare two text files, like for instance PHP, HTML, ASP, to determine which lines are different. It can also highlight the differences ...
www.phpclasses.org/browse/package/2365.html - Similar pages

Good luck, this is a good exercise.

Note - currently you have no way of indicating a word in the first phrase doesn't exist in the second - don't know if you need to show that change.

OwenTheSamoan

Seems a bit more complicated than I thought it would be. I will look into this further. Thank you for steering me into the right direction with the site links.