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1 loop too many in array iteration

by jms53 (Monk)
on Feb 13, 2013 at 08:17 UTC ( #1018500=perlquestion: print w/replies, xml ) Need Help??
jms53 has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks,

Having followed your advice, my simple object is now working. However, I don't understand why the code works as it is.

I have an object, with the following structure:
sub new { my ($class, %attr) = @_; my $ref = \%attr; my @history; $ref->{history} = \@history; }
I then have a method that pushes an array-ref to @{$ref->{history}}:
sub trans { my @done = ["$time[5]-$time[4]-$time[3]", $type, $amount]; push @{$self->{history}}, \@done; }

My problem comes to when I want to see the contents of $self->{history}, I have to use 3 loops, when it's only a 2-dimensional array.

sub statement { #iterate through @{$self->{history}} in 2 dimensions my $self = shift; for my $index ( 0..$#{ $self->{history} } ) { for my $j (0..$#{$self->{history}[$index] } ) { for (0..$#{$self->{history}[$index][$j] } ) { print "$self->{history}[$index][$j][$_]\t"; } print "\n"; } } }

If anyone could explain to me why the need for 3 loops (or show me where my de-referencing went awfully wrong), it would be greatly appreciated.

J -

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Re: 1 loop too many in array iteration
by Athanasius (Chancellor) on Feb 13, 2013 at 08:23 UTC

    Square brackets [] return a reference to an array — i.e., a single scalar value. So the line:

    my @done = ["$time[5]-$time[4]-$time[3]", $type, $amount];

    assigns an array reference to the first element only ($done[0]) of @done. I think you wanted:

    my @done = ("$time[5]-$time[4]-$time[3]", $type, $amount);

    which populates the array @done with three scalar values.

    Hope that helps,

    Athanasius <°(((><contra mundum Iustus alius egestas vitae, eros Piratica,

Re: 1 loop too many in array iteration
by tmharish (Friar) on Feb 13, 2013 at 09:44 UTC

    Your new does not have a bless.

    Did you leave that out of the code fragment here?

Re: 1 loop too many in array iteration
by vinoth.ree (Monsignor) on Feb 13, 2013 at 09:27 UTC


    jms53 if the loop goes like this you try to print your data structure using Data::Dumper module, so that you can get understand how the data get saved.

      I didn't see the structure any different from what I was expecting in Data::Dumper, although that is likely to be my lack of experience with Data::Dumper.

      Athanasius's correction to the sub made everything work as expected.

      Thanks for all the help and wisdom!
      J -

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