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

That is certainly != to what I wrote....

Exactly the point. In your code, each iteration of the loop assigns the next row to $_ (your while statement), then assigns the following line to $line_holder. The line assigned to $_ is never handled, so it just get's "skipped."

In any case, couldn't the whole process be reduced to

my %seen = () ;
my @uniq_rows = grep { !$seen{$_}++ } <FILE> ;
[download]

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DamnDirtyApe

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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
Er just a thought but any time ive written that code ive ended up changing it to `my @unique=map{chomp; $_{$_}++ ? () : $_} <FILE>;` [download] 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)	[reply] [d/l]
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;` [download] 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> );` [download] 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... :-)	[reply] [d/l] [select]
Re: Re^6: Unique array w/o repeated elements and still keep the original order! by demerphq (Chancellor) on Aug 09, 2002 at 21:28 UTC
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)	[reply]


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