in reply to Code clarification - use of map and $$_

while (<IN>) {
    our(@F) = split(/\s+/, $_, 0);
    push @{$r{join ' ' x 8, @F[0..3]};}, [@F[4, 6]];
    sub END {
        foreach $k (keys %r) {
            my($x, $y);
            map {$x += $$_[0]; $y += $$_[1];} @{$r{$k};};
            my @g = split(/\s+/,$k);
            print OUT "$g[0]\t@g[1]\t@g[2]\t@g[3]\t", $x / scalar(@{$r
+{$k};}), "\t$y\n";
        }
    }
}

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Another odd thing to note about this code is the  END block planted in the middle of it, written in a disparaged way as a sub block. Please see the "BEGIN, UNITCHECK, CHECK, INIT and END" section in perlmod. Because all  END blocks run at the end (!) of all other code, I think this chunk of code could more clearly and conventionally be written as: 

while (<IN>) {
    our(@F) = split(/\s+/, $_, 0);
    push @{$r{join ' ' x 8, @F[0..3]};}, [@F[4, 6]];
}

... all other code ...

END {
    foreach $k (keys %r) {
        my($x, $y);
        map {$x += $$_[0]; $y += $$_[1];} @{$r{$k};};
        my @g = split(/\s+/,$k);
        print OUT "$g[0]\t@g[1]\t@g[2]\t@g[3]\t", $x / scalar(@{$r{$k}
+;}), "\t$y\n";
    }
}

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Good luck.

Give a man a fish:  <%-{-{-{-<

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Re^2: Code clarification - use of map and $$_
by pryrt (Abbot) on Aug 09, 2016 at 15:16 UTC

    ++AnomalousMonk: that helped (me, anyway; don't know about the OP). That was my first guess, but my initial experiments with the OP code didn't mesh. But I later saw that the print went to OUT, and forgot to redo a test to STDOUT. Thus I started thinking that it was a sub named END in a bout of horrible style. But I think you're right, it's an END block.

    However, with this simplified code, I still only see the FIRST instance of the END block doing anything:

    use strict;
use warnings;

$, = ",";
$\ = "\n";
$" = ";";

my %r = ( 0 => 0, 1 => 0, 2 => 0, 3 => 0 );

foreach (1..10) {
    my $x = $_ % 4;
    ++$r{$x};
    sub END { print __LINE__, "sub END block", $x, $r{$x} };
}

foreach(1 .. 10) { my $x = $_ % 4; print "$_ => $x => $r{$x}"};
print __LINE__, "END OF SCRIPT";
__END__
__OUTPUT__
1 => 1 => 3
2 => 2 => 3
3 => 3 => 2
4 => 0 => 2
5 => 1 => 3
6 => 2 => 3
7 => 3 => 2
8 => 0 => 2
9 => 1 => 3
10 => 2 => 3
17,END OF SCRIPT
13,sub END block,1,3

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      ... I still only see the FIRST instance of the END block doing anything ...

      From this I think you've already gotten the point, but anyway... There is only one instance of any given  END block in a program: 

      c:\@Work\Perl\monks>perl -wMstrict -le
"for my $str (qw(one two three)) {
   print qq{in for loop: '$str'};
   END { print 'END block ONE';   }
   END { print 'END block TWO';   }
   END { print 'END block THREE'; }
   }
"
in for loop: 'one'
in for loop: 'two'
in for loop: 'three'
END block THREE
END block TWO
END block ONE

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      Give a man a fish:  <%-{-{-{-<

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      Oops, re-reading AnomalousMonk's post and the OP, I was reminded that there was a loop inside the END block, and that does what was intended.

      use strict;
use warnings;

$, = ",";
$\ = "\n";
$" = ";";

my %r = ( 0 => 0, 1 => 0, 2 => 0, 3 => 0 );

foreach (1..10) {
    my $x = $_ % 4;
    ++$r{$x};
    sub END {
        $, = " => ";
        foreach my $k ( keys %r ) {
            print __LINE__, "sub END block with k", $k, $r{$k}
        }
    };
}

foreach(1 .. 10) { my $x = $_ % 4; print "$_ => $x => $r{$x}"};
print __LINE__, "END OF SCRIPT";
__END__
__OUTPUT__
1 => 1 => 3
2 => 2 => 3
3 => 3 => 2
4 => 0 => 2
5 => 1 => 3
6 => 2 => 3
7 => 3 => 2
8 => 0 => 2
9 => 1 => 3
10 => 2 => 3
22,END OF SCRIPT
16 => sub END block with k => 0 => 2
16 => sub END block with k => 1 => 3
16 => sub END block with k => 3 => 2
16 => sub END block with k => 2 => 3

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