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

##</code><code>##

my $r2;
my $flipper = 0;
for( @$r ) {
  if( $flipper++ % 2 ) {
    push @{$r2->[$#{$r2}]}, $_;
  }
  else {
    push @$r2, [ $_ ];
  }
}

##</code><code>##

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

##</code><code>##

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

##</code><code>##

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

##</code><code>##

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

##</code><code>##

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

##</code><code>##

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

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

##</code><code>##

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

##</code><code>##

#! /usr/bin/perl -w

use strict;
use Benchmark qw/cmpthese/;
use Data::Dumper;

$Data::Dumper::Indent = 0;

my $iters = shift || 1000;
my $len   = shift || 8;

sub flipper {
	my @r2;
  my $flipper = 0;
  for( @_ ) {
    if( $flipper++ % 2 ) {
      push @{$r2[$#r2]}, $_;
    }
    else {
       push @r2, [ $_ ];
    }
  }
  \@r2;
}

sub map_i {
  my $i = 0;
  [ map { [$_[$i*2], $_[$i++*2+1]] } (0 .. scalar(@_)/2 - 1) ];
}

sub shifter {
  my @r2;
  while( @_ ) {
    push @r2, [ shift @_, shift @_ ];
  }
  \@r2;
}

sub c_loop {
  my @r2;
  for( my $i=0; $i < scalar @_; $i += 2 ) {
    push @r2, [ @_[$i, $i+1] ]
  }
  \@r2;
}

sub map_pure {
  [ map{ [$_[$_*2], $_[$_*2+1]] } (0 .. scalar @_ / 2 - 1) ];
}

sub aslice {
  my @r2;
  $r2[$_] = [ @_[$_*2, $_*2+1] ] for (0 .. scalar @_ / 2 - 1);
  \@r2;
}

sub map_jm {
  [ map { [$_[2*$_], $_[2*$_+1]] } 0 .. scalar @_ / 2 - 1 ];
}

sub map_jm2 {
  [ map { [@_[2*$_, 2*$_+1]] } 0 .. scalar @_ / 2 - 1 ];
}

sub splicer {
  my @r2;
  while (my @pair = splice @_, 0, 2) {
    push @r2, [@pair];
  }
  \@r2;
}

######################################################

my $r = [ 1 .. $len ]; 
for my $sub( qw/ flipper shifter splicer c_loop aslice
    map_i map_pure map_jm map_jm2 /) {
  no strict 'refs';
  # test
  # print "$sub ", Dumper( &$sub( @$r )), "\n";
}

cmpthese(
  $iters,
  {
    flipper  => sub { flipper( @$r )},
    shifter  => sub { shifter( @$r )},
    splicer  => sub { splicer( @$r )},
    c_loop   => sub { c_loop( @$r )},
    aslice   => sub { aslice( @$r )},
    map_i    => sub { map_i( @$r )},

    map_pure => sub { map_pure( @$r )},
    map_jm   => sub { map_jm( @$r )},
    map_jm2  => sub { map_jm2( @$r )},
  },
);
__END__