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Re: Sorting a "tuple" by the second value

by Anonymous Monk
on Apr 09, 2012 at 04:17 UTC ( #964077=note: print w/ replies, xml ) Need Help??

Comment on Re: Sorting a "tuple" by the second value
Re^2: Sorting a "tuple" by the second value
by thmsdrew (Scribe) on Apr 09, 2012 at 04:53 UTC

    Thanks for that link, it was helpful for sure. Here's how I did it. The first subroutine gets the tuples from the file, splits them into an array, and writes them all into one array.

    sub get_links { my @links; open(my $fh, "<", "links.alpha.sorted.25sample") or die "cannot open < links.alpha.sorted.25sample: $!"; while(<$fh>) { chomp; my $tuple; @$tuple = split(/\s+/, $_); push(@links, $tuple); } return @links; }

    Then I sort by the second value and write it to another file:

    sub sort_and_store { my @links = get_links(); my @sorted_links = sort { $a->[1] cmp $b->[1] } @links; open(my $fh, ">", "sorted.by.destination") or die "cannot open > sorted.by.destination: $!"; foreach my $tuple (@sorted_links) { print $fh "@$tuple\n"; } }

    I've never used the @$blah variable type before, and I couldn't find any information about it. I'm guessing that's how you refer to the arrays in an array of arrays?

      I've never used the @$blah variable type before, and I couldn't find any information about it. I'm guessing that's how you refer to the arrays in an array of arrays?

      Yes, that is one way to do it, known as dereferenceing because $blah is a reference, see references quick reference

      Its nice you picked up a new trick, but I would still use sort :)

      $ cat fafafile 3 6 1 1 2 0 9 1 9 4 4 5 7 3 2 0 5 4 6 7 6 2 9 8 $ sort --dictionary-order fafafile 0 5 4 1 2 0 2 9 8 3 6 1 4 4 5 6 7 6 7 3 2 9 1 9 $ sort --dictionary-order --key=2,2 fafafile 9 1 9 1 2 0 7 3 2 4 4 5 0 5 4 3 6 1 6 7 6 2 9 8

        Wow, that is a lot easier than my way. It takes longer but I also had to take the time to write the program in the first place! Thank you kind sir!

      You could combine the steps in your get_links() and sort_and_store() subroutines into one process.

      knoppix@Microknoppix:~$ cat spw964070.in abc peter def jack ghi zak jkl ben mno mick pqr alan knoppix@Microknoppix:~$ perl -Mstrict -wE ' > open my $inFH, q{<}, q{spw964070.in} > or die qq{open: < spw964070.in: $!\n}; > open my $outFH, q{>}, q{spw964070.out} > or die qq{open: > spw964070.out: $!\n}; > > print $outFH > map { $_->[ 0 ] } > sort { $a->[ 2 ] cmp $b->[ 2 ] } > map { [ $_, split ] } > <$inFH>; > > close $inFH > or die qq{close: < spw964070.in: $!\n}; > close $outFH > or die qq{close: > spw964070.out: $!\n};' knoppix@Microknoppix:~$ cat spw964070.out pqr alan jkl ben def jack mno mick abc peter ghi zak knoppix@Microknoppix:~$

      Sticking to your subroutines, it would be more efficient for get_links() to return a reference to @info than the huge array itself, like so:-

      ... return \ @links; } sub sort_and_store { my $refToLinks = get_links(); my @sorted_links = sort { $a->[1] cmp $b->[1] } @$refToLinks; ...

      I hope these points are helpful.

      Cheers,

      JohnGG

        Definitely helpful. I need to learn more about referencing and when it's best to use. Thanks!

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