I had to create a report of the differences between two files each containing thousands of unsorted records. I *thought* that I needed some form of Diff. I tried Algorithm::Diff, but discovered that it only works line-by-line. For instance, Algorithm::Diff reports that (1,2,3) and (2,1,3) are different lists.

Furthermore, some commercial tools I tried did the same thing.

I accidentally stumbled across List::Compare, which was lucky for two reasons.

Most importantly, List::Compare solved my problem, and more: it shows intersections and unions of sets; it shows elements unique to either list (that was my particular problem); it shows all unique elements of both lists, and even all elements of both lists. The interface is elegant and intuitive. I'll be dealing with large inventory lists well into the future, and List::Compare is shaping up to be my tool of first resort for all my list comparison needs.

I was also lucky because James Keenan gives a detailed history of the source (Perl Cookbook) and the circumstances (introductory Perl course) that inspired him to write the module, as well as pointing out a number of similar modules, just in case List::Compare doesn't solve your particular problem. I am relatively new to Perl, and I don't entirely grok the power of hashes yet. List::Compare not only allowed me to solve my immediate problem quickly and elegantly, but it also showed me how to understand the code that underlies the List::Compare module itself.

Elegant, intuitive, well-documented, and with great hints about the magic behind the module. I'm glad I found List::Compare, and you probably will be, too.

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.