in reply to At each change in...

Well, if you are on a Unix system, make use of its toolkit. One of the tools is called sort and usually has options to "merge, do not sort" and "uniques only". On my system, you these options are enable with -mu, but check your manual page. Then, instead of opening your file with: 
    open my $fh => "file" or die $!;

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open it with: 
    open my $fh => "sort -mu file |" or die $!;

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No counter needed, no check, no keeping track of the previous. Ultimate code reuse.

Abigail

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Re: Re: At each change in...
by stefp (Vicar) on Jun 13, 2002 at 11:41 UTC
    For me, the whole point of perl is to be able to forget this Unix stuff by getting inside one hood. Perl is the (almost) the same on every platform. And the effort to learn perl is offset by being able to forget this myrad of Unix commands with myriad of options that are supported or not on a given platform. Also there is often overhead avoided by perl. In the case at hand, we have to fork and pipe (no big deal) and sort (this last can cost if the processed file is very big)

    But again, TMTOWTDI.

    -- stefp -- check out TeXmacs wiki

[reply]
      Is having to learn a myriad of Unix command worse than having to learn a myriad of APIs of a myriad of Perl modules? Or do you plan to do everything yourself? I rather reuse what others have done....

      Note also that IEEE Std 1003.1 - 2001 (aka POSIX) "Shell and Utilities" require the -m and -u options.

      As for the overhead of sort, in the given example, no sort is actually done. The -m option, for merge, merges files which are already presumed to be sorted - but when given one file, this passes things unsorted.

      Abigail

[reply]
        It so easy to do some things in Perl that very often, I don't even think of using external commands or exotic modules so my code is independant of anything but a vanilla Perl installation. I learn Perl in 1989 for that very reason: to forget about sed, cut, sort (...) while getting the benefit to already know since perl was conceptually reaped from them.

        you don't need a sort because you assume your file(s) sorted; what a specious argument!!

        -- stefp -- check out TeXmacs wiki

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Re: Re: At each change in...
by ariels (Curate) on Jun 13, 2002 at 12:26 UTC
    Why not just use the program uniq? It would appear to perform the same function as you desire, and is perhaps more recognizable when reading.
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      uniq works as well; my point was more about using the toolkit available then sort vs uniq.

      Abigail

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