in reply to Summing Up Array Elements By Group

I might not be effective!, but a solution here. 
my @arr = (0,0,1, 3,2,0, 1,1,1, 11,100,12);
push (@Res, eval join("+",splice(@arr,0,3))) while (@arr/3);
print "@Res";

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Re^2: Summing Up Array Elements By Group
by ikegami (Patriarch) on Jan 21, 2009 at 14:58 UTC

    eval EXPR? oh my! No, use sum! 

    use List::Util qw( sum );
push @Res, sum splice(@arr,0,3) while @arr;

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[d/l]
[select]
      Thank you, ikegami, but one more question on this,
      I have seen the Util.pm code and I included only the reduce and sum part into the below code, now the code looks like this. 
      sub reduce (&@) {
  my $code = shift;
  no strict 'refs';

  return shift unless @_ > 1;

  use vars qw($a $b);

  my $caller = caller;
  local(*{$caller."::a"}) = \my $a;
  local(*{$caller."::b"}) = \my $b;

  $a = shift;
  foreach (@_) {
    $b = $_;
    print ">$code<\n";
    $a = &{$code}();
  }

  $a;
}
use vars qw($a $b);
sub sum (@) { reduce { $a + $b } @_ }
@arr = (0,0,1, 3,2,0, 1,1,1, 11,100,12);
push @Res, sum splice(@arr,0,3) while @arr;
print "@Res\n";

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      Now I see the magic part is '&{$code}()', could you please explain me about this magic part and tell me how this is better than eval?.
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        Converting user inputs to Perl code safely is tricky and if dangerous if you fail. When using sum, nothing from the user is converted to Perl code and executed.

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