Wdiff compare – Good!

Wdiff compare – Good!

[update Dec 2010: click here for my attempt at an online comparison service.]

(see also: Real World Test, Docdiff post, OOo compare post)

I previously commented (adversely) on the performance of OpenOffice.org’s compare function.   Tridge suggested that I might try wdiff – and I’m pleasantly surprised.  When I ran wdiff on the two text files I used in that post it gave me this:

[-1.1Contractor-]{+1.1[Vendor]+} may invoice [-[Customer]-] {+Customer the Fees for each Service in accordance with the Payment Terms and, where no relevant time is set out in the Payment Terms, [Vendor] may invoice the Customer+} for ongoing fees quarterly in [-arrears-] {+advance+} and other fees [-monthly-] in arrears.  [-Contractor must-]  {+[Vendor] will+} provide [-[Customer]-] {+Customer+} with a tax invoice in respect of all GST charged.  [-[Customer] is not liable to pay any amount in respect of GST except as set out in a valid tax invoice.-]

Which, if you can decipher the inline formatting instructions, is a better performance than OOo (not that that would be difficult mind…).  In fact, if I’m reading it correctly, it seems to be only slightly worse than the output of Word’s compare (it marks changes within “words” as a change of a word – so the  [-[Customer]-] {+Customer+} is not a minimal change set- it should be  [-[-] and [-]-]).  I will try to find sometime to test it on longer clauses or whole agreements.  A bonus is that its output format is cut-and-paste compatible, albeit a little visually unappealing.  It shouldn’t be too much trouble to pipe it through something to pretty it up (the -p option apparently prints overstrikes, but this doesn’t work on my tty – ah, -t is what i need for more visual output on a tty).  A second bonus is that -s gives change statistics (I don’t recall ever seeing this in Word).

The other nice thing about wdiff is that it was already installed on my machine!  About two (maybe three??) years ago I googled around for something that would do diffs on text files, but the searches only showed diff, kdiff etc.  Wdiff apparently dates back to the early 90s so my search terms maybe weren’t the best – or too many other people are using and linking to diff!  Anyway, wdiff seems to be part of the standard install for OpenSuSE and I’d had it all along.

And thanks Tridge!

Update:

Tridge says:

There are probably quite a few other similar utilities. Minimal diff
algorithms are a nice little computer science task. I'm sure heaps of
people have written variants. I expect quite a few CS courses use this
sort of thing as an exercise for 2nd year programming students...

Improving the algorithms in OOo would be a nice Google summer of code
project.

Which I think would be a great idea and a valuable addition to OOo.  If anyone’s game to try (either as a student or a supervisor) please drop me an email or lodge a comment and I’ll try to connect you.

Update 2:

Following someone’s suggestion, I have tried meld – am impressed by the interface, but not by the markup.  Run on the same two sample text files it marked:

with a tax invoice in respect of all GST charged.

as unchanged, with the balance as deletion/addition.  Sadly, this is a better performance than OOo (but is still inadequate).