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  for @$r -> $x, $y {
    push @$pairs, [$x, $y];
  }

my $r2;
my $flipper = 0;
...
    push @$r2, [ $_ ];
  }
}

my %h=(@$r);
for (keys %h) {
...
}
# or possibly
# push @$r2, [$_, $h2{$_} ] for keys %h

my $i = 0;
my $r2 = map {[ $r->[$i*2], $r->[$i++*2+1] ]}
         (0 .. $#{$r}/2 - 1);
    # or (0 .. scalar(@$r)/2 - 1)

for( my $i=0; $i < scalar @$r; $i += 2 ) {
  $r2->[$i/2] = [ @$r[$i, $i+1] ]
}

my @copy = @$r;
for( @copy ) {
    push @$r2, [ $_, shift @copy ];
}

my @copy = @$r;
while( @copy ) {
    push @$r2, [ shift @c, shift @c ];
}

  $r2 = [ map { [$r->[2*$_], $r[2*$_+1]] } 0 .. scalar @$r / 2 - 1 ]

  $r2 = [ map { [@$r[2*$_, 2*$_+1]] } 0 .. scalar @$r / 2 - 1 ]

@copy = @$r;
while (my @pair = splice @copy, 0, 2) {
  push @$r2, [@pair];
}

#! /usr/bin/perl -w

...
  },
);
__END__