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Re^2: Uniq and sort in perl

by slayedbylucifer (Scribe)
on Jul 12, 2012 at 09:22 UTC ( #981339=note: print w/ replies, xml ) Need Help??

in reply to Re: Uniq and sort in perl
in thread Uniq and sort in perl

Utilitarian, I can't thank you enough. Your solution is **exactly** what I was looking for. Thank you very Much !!

But, unfortunately i am not able to decode or understand your oneliner. Could you guide me to some documentation for the same.

Thanks Again for the lightning fast response.

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Re^3: Uniq and sort in perl
by Anonymous Monk on Jul 12, 2012 at 10:51 UTC
Re^3: Uniq and sort in perl
by Preceptor (Deacon) on Jul 15, 2012 at 11:26 UTC
    What is happening in that one liner:
    print "$vm, $filer, \n" if ! $seen{"$vm:$filler"}++

    It's quite an elegant piece of code, with a lot going on. So let's break it down:

    • The hash called '%seen' is being checked - to see if it contains a key called "$vm:$filler". The value of this is being tested for being 'false'. (because there's 'if !' which is 'if not') - which is literally 'if not seen'
    • So if $seen{"$vm:filler"} is _not_ 'true' - we haven't seen it, and so we print it.
    • And then that ++ kicks in, to post increment, 'adding one' to $seen{"$vm:$filler"}' - so the first time we try doing that, it's going to be undefined (and thus false) triggering a print. Second time, it'll be 'non zero' and so evaluate as 'true'.
    For bonus points, you can probably do:
    foreach my $key ( keys %seen ) { print "$key was seen $seen{$key} times\n"; }
    Does that make it any clearer?

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