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Re: Re: Re: Re: Re: Unique array w/o repeated elements and still keep the original order!

by demerphq (Chancellor)
on Aug 09, 2002 at 21:05 UTC ( #189048=note: print w/ replies, xml ) Need Help??


in reply to Re: Re: Re: Re: Unique array w/o repeated elements and still keep the original order!
in thread Unique array w/o repeated elements and still keep the original order!

Er just a thought but any time ive written that code ive ended up changing it to

my @unique=map{chomp; $_{$_}++ ? () : $_} <FILE>;
or something like it (i dont always use %_ but sometimes i do, blame ABIGAIL-II ;-)

To be honest i think that in my perl career ive only used a grep a few times. map seems to be so much more useful in that it can do grep()s job, and more as well!

Yves / DeMerphq
---
Software Engineering is Programming when you can't. -- E. W. Dijkstra (RIP)


Comment on Re: Re: Re: Re: Re: Unique array w/o repeated elements and still keep the original order!
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Re^6: Unique array w/o repeated elements and still keep the original order!
by jynx (Priest) on Aug 09, 2002 at 21:17 UTC

    And when i write something like that i usually change it to something like:
    my %seen; my @unique = grep {not $seen{$_}++} <FILE>; chomp @unique;
    Or something similar. It might not be the best way to do it, but it has one advantage...

    It has nothing to do with using %_. It's mostly because i'm very wary of changing $_ in map, especially since i recently got very burned by attempting such a thing...

    jynx

    update: at prompting, i'll mention that one could write that as:

    my (%seen, @unique); chomp( @unique = grep {not $seen{$_}++} <FILE> );
    however, i think that would iterate twice as well. Then again there's that point about premature optimization... ;-)

    Update 2: after doing a benchmark, i've found that the map solution is the fastest, followed by the one-line chomp and last is the two-liner. The one-liner is sufficiently fast enough that i would still prefer it, although for readability and maintainability i might still go with the two line version. To each their own...

    Thanks demerphq for the learning experience... :-)

      Heh, its to avoid the code you posted (and the implicit overhead of going through the list twice) that makes me use map{} instead.

      I assume you somehow tried to change the value of constants or something like that?

      BTW, i know the above could be represented as premature optimization, but the idea of iterating over a list twice for no good reason makes me unhappy.

      :-)

      Yves / DeMerphq
      ---
      Software Engineering is Programming when you can't. -- E. W. Dijkstra (RIP)

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