Slash Boxes
NOTE: use Perl; is on undef hiatus. You can read content, but you can't post it. More info will be forthcoming forthcomingly.

All the Perl that's Practical to Extract and Report

use Perl Log In

Log In

[ Create a new account ]

Purdy (2383)

AOL IM: EmeraldWarp (Add Buddy, Send Message)
Yahoo! ID: jpurdy2 (Add User, Send Message)

Bleh - not feeling creative right now. You can check me out on PerlMonks [].

Journal of Purdy (2383)

Wednesday September 07, 2005
08:24 AM

IRC Hacking

[ #26626 ]

So I was on #cgiapp ( and Cees Hek taught me a few things, one involving lists, arrays and scalars.

Have you ever tried this?
@a=('one','two','three'); $b = @a; print $b;

So what's the output? '3' ... I knew that and my world was safe & sheltered. Then Cees threw this one at me:
$b = ('one','two','three');print $b;

What's that output? '3'? ... Nope, it's 'three', the last element of the list.

insert sound of head exploding

Before moving on, I think this is a good example of how such a truth of life can really alter your worldview. Not just in Perl, but when you learn something new like that, it really breaks your grip on "reality" and takes a moment (or two) to readjust and get a new grip. I encourage a good shake-up every once in a while.

Ok, so then I was head-coding while playing with Meredith (she's so cute), getting around a CSV file that I will need to import into a database and it has rows with ID #'s and then a column in a row for other ID #'s that are the same 'entity'. So I plan on consolidating them into my shiny new relational db. So I'll need something to determine if the ID # is the minimal # of the set - if so, it's a new 'entity' record. Otherwise, associate the new record w/ the minimal number.

So I'll have the ID # and a list of other ID #'s and I need to know if it's the smallest.

So then I said to myself ... what if I used that concept that Cees taught me w/ a reverse sort? Like:
if ( $id_number == reverse sort @ids )

There are some context issues there that I couldn't (and still don't all that well) understand. Cees nailed it, though:
if ( $id_number == @{[reverse sort @ids]}[0..$#ids] )

Pretty cool, huh? I call it the Hek-Purdy min(). Or maybe "a Hek of a Purdy-good min() function" (helps if you say that in a Southern accent ;)).

Now this is not very readable or maintainable, so I don't plan on world-wide deployment - just my import script ... for now. ;)



The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
More | Login | Reply
Loading... please wait.
  • So I'll have the ID # and a list of other ID #'s and I need to know if it's the smallest.
    You went a very convoluted route to do this:
    if ( $id_number == (sort @ids)[0] )
    Learn about literal slice: (LIST)[INDICIES]. We document it in Learning Perl.
    • Randal L. Schwartz
    • Stonehenge
    • *grin* - yeah, I know. I should have put a * next to "good" - I'm not endorsing that as THE way: TIMTOWTDI and all that. And your approach is definitely cleaner ... I was just thinking about how to incorporate what I learned about scalarizing a list.


  • So I'll have the ID # and a list of other ID #'s and I need to know if it's the smallest.

    That code is very confusing. Sorta like taking a flight from NY to LA by via Johannesburg and Perth. Why not just grab the smallest element of the list?

    use List::Util qw(min);

    if ( $id_number == min(@ids) )

    If you needed to avoid List::Util for some odd reason, I don't know why you would sort a list, reverse it and take the last element (in a most convoluted fashion) when you could just:

    if ( $id_number =

    • *nod* - agreed. See prev. comment - I simply wanted to apply what Cees taught me about scalarizing a list.

      Hmmm -- maybe this won't even see the light of day in my import script now. ;)


  • I thought it was common knowledge that there is no such thing as a list in scalar context. :-)

    The context issues are particularly important when you return things. my $foo = bar(); will produce a different result with a bar function that does return @arr; vs one that does return ( $baz1, $baz2, $baz3 ). This is even more insidious if you do something like return grep quux($_), @arr.

    Always mind your context.

    Your particular example, btw, besides all the issues already pointed out by others, should at l