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array bug?

by sacadura (Initiate)
on Feb 03, 2003 at 18:26 UTC ( [id://232340]=perlquestion: print w/replies, xml ) Need Help??

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Re: array bug?
by broquaint (Abbot) on Feb 03, 2003 at 18:43 UTC
    This is nothing to do with arrays but how sort processes it's arguments, which is lexically (as opposed to numerically as you were expecting). Here's the relevant paragraph from the sort docs
    Sorts the LIST and returns the sorted list value. If SUBNAME or BLOCK is omitted, "sort"s in stan- dard string comparison order. If SUBNAME is spec- ified, it gives the name of a subroutine that returns an integer less than, equal to, or greater than "0", depending on how the elements of the list are to be ordered. (The "<=>" and "cmp" operators are extremely useful in such routines.) SUBNAME may be a scalar variable name (unsub- scripted), in which case the value provides the name of (or a reference to) the actual subroutine to use. In place of a SUBNAME, you can provide a BLOCK as an anonymous, in-line sort subroutine.



Re: array bug?
by hding (Chaplain) on Feb 03, 2003 at 18:39 UTC
    I'm not sure why you think this is a bug, as you do not say. It appears to be working correctly to me; perhaps the piece of information that you lack is that sort by default sorts things as strings, which you could discover by reading the documentation for sort. If you want to sort numerically, you can supply your own function or block to do it.
Re: array bug?
by ChemBoy (Priest) on Feb 03, 2003 at 18:43 UTC

    You don't specify what you think the bug is, but I'm going to assume you're surprised by the sort order. If so, you should reread the documentation on sort: unless you tell it otherwise, it sorts by string comparison, rather than numeric comparison. Since the character value for 3 is less than that of 8, "30" is less than "8" (but greater than "08", of course).

    To get the result you're probably looking for, try

    foreach (sort {$a <=> $b} @arr) {... }

    If God had meant us to fly, he would *never* have given us the railroads.
        --Michael Flanders

Re: array bug?
by Fletch (Bishop) on Feb 03, 2003 at 18:38 UTC

    No bug, last time I heard, `4' came before `8'.

    Hint: perldoc -f sort

Re: array bug?
by LAI (Hermit) on Feb 03, 2003 at 18:46 UTC

    This isn't a bug, it's a feature.

    What's happening is that the numbers are getting sorted as strings, and since 8 comes after 30 (chr(8) > chr(3)) (ord(8) > ord(3)), you get those unwanted effects.

    Fortunately, (hurrah!) you can pass additional sorting methods to sort. For instance, reverse sort @arr can be rewritten as sort {$b cmp $a} @arr. You can use the same feature to sort numerically using the UFO operator: sort {$a <=> $b} @arr

    There's other ways sort simplifies your life; RTFM for more info.

    Update: Successfully picked; thanks, ChemBoy... although what I wrote is technically true as well... :o)


      Nit: I believe you want ord, not chr. :-)

      If God had meant us to fly, he would *never* have given us the railroads.
          --Michael Flanders

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