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Re: Hash keys affect sorting

by TedPride (Priest)
on Jul 07, 2006 at 15:57 UTC ( #559815=note: print w/ replies, xml ) Need Help??


in reply to Hash keys affect sorting

I must be missing something here, but why use a hash structure at all? Just put your data into an array, then if you want to be able to access the array based on certain keys, create a hash indexes for just those keys:

use strict; use warnings; my (@data, %identifier); while (<DATA>) { chomp; @_ = split /\s+/, $_, 6; push @data, [@_]; $identifier{$_[0]} = $data[-1]; # Index for first field } # Sort on multiple fields, in this case fifth and first... print "@$_\n" for sort {$a->[4] cmp $b->[4] || $a->[0] <=> $b->[0]} @d +ata; __DATA__ 1 1023 T C cc Item 1 2 1560 T C aa Item 2 3 9102 T C bb Item 3 4 11222 T C ff Item 4 7 13456 T C bb Item 7


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Re^2: Hash keys affect sorting
by 0xbeef (Hermit) on Jul 07, 2006 at 22:00 UTC
    I'm a baby monk only... ;)

    Have to admit I have never seen @_ used for anything else than for function arguments, and I don't exactly understand push @data, [@_]; Using @_ seems nice and intuitive, applying it to my example gives me:

    use strict; my $output = <<EOD; 4865FA9B 0702 P H rmt0 TAPE OPERATION ERROR DE9A52D1 0704 I S rmt0 DEVICE DUMP RETRIEVED 4865FA9B 0701 P H rmt2 TAPE OPERATION ERROR F3E9B3E2 0620 I O SYSJ2 UNABLE TO ALLOCATE SPACE IN FILE SY +STEM DCB47997 0511 T H hdisk4 DISK OPERATION ERROR EOD my (@data, %identifier); for my $line (split /\n/,$output) { @_ = split /\s+/, $line, 6; push @data, [@_]; $identifier{$_[0]} = $data[-1]; # Index for first field } # Sort on multiple fields, in this case 4th (class) and 2nd (time)... print "\@data:\n"; for my $rec (reverse sort {$a->[3] cmp $b->[3] || $a->[1] <=> $b->[1]} + @data) { print "Error ID: $rec->[0] Time: $rec->[1]\n"; }

    Also, if i understand you right, %identifier contains a hash of array references which I can use to access @data elements e.g.

    print "key $_ value: $identifier{$_}->[0]\n" for (keys %identifier);

    Thanks for the help!

    Niel

      $_ is to scalar what @_ is to array and %_ is to hash, although %_ is seldom seen in the wild.

      push @data, [@_] means: $_ was split into @_; if they said push @data, @_ the array @_ would append it's elements to @data. To append @_ as one unit to @data it must be given boundaries [ ]; this construct creates an array reference. This reference (a scalar) is stored in @data, holding the elements of @_ which are copied into [ ] at the moment of creation of [ ]. See perlreftut. Think of [@_] as "scalarifying" @_ into an (anonymous) array reference; an array can only hold scalars (single values, which references happen to be).

      Wow. What noise ;-)

      hoping not to have confused you further,
      --shmem

      _($_=" "x(1<<5)."?\n".q/)Oo.  G\        /
                                    /\_/(q    /
      ----------------------------  \__(m.====.(_("always off the crowd"))."
      ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

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