husker has asked for the wisdom of the Perl Monks concerning the following question:

I would like to output some data in columnar form, but I can't figure out how to write the format statement to do it. I'd like it to look something like this: 
Mike   456            Bob    568
Sally  594            Bubba  102

[download]
I know a format statement like: 
@>>>>>> @###          @>>>>>> @####
$a1,    $b1,          $a2,    $b2

[download]
would work, but that would mean I'd have to process my hash that has my data two elements at a time so I could set $a1, $b1, $a2, and $b2 explicitly.

Perl has so many "lazy" shortcuts ... is there a simpler way to do columnar output using formats?

Replies are listed 'Best First'.
Re: Using formats for 2-columnprinting
by merlyn (Sage) on Oct 03, 2000 at 18:05 UTC
    Untested except by running it in the version of Perl installed in my head: 
    {
  my $value;
  my $hash_ref;
  my $done;
  sub get_key {
    unless ($done) {
      (my $key, $value) = each %$hash_ref or # yes, $value is out of s
+cope
        $done = 1;
    }
    defined $key ? $key : "";
  }
  sub get_value {
    defined $value ? $value : "";
  }
  sub set_hash {
    $hash_ref = shift;
    keys %$hash_ref; # reset each()
    $done = 0;
  }
}

set_hash(\%hash_you_want_to_scan);
write STDOUT;

format STDOUT =
@>>>>> @###     @>>>>> @### ~~
get_key(), get_value(), get_key(), get_value()
.

    [download]
    Note the use of the repeating format line to execute that value as long as data is available, then stop when it's not.

    -- Randal L. Schwartz, Perl hacker

    update: Change that middle subroutine to: 
      sub get_key {
    my $key;
    unless ($done) {
      ($key, $value) = each %$hash_ref or # yes, $value is out of scop
+e
        $done = 1;
    }
    defined $key ? $key : "";
  }

    [download]
    Too early in the morning for this. {grin}
    update 2: Yes, those @#### need to be changed to @<<<< as well. Thanks for actually running the code, jcwren!
[reply]
[d/l]
[select]
      I tried what you wrote, just for grins. I had to change the get_key() routine slightly to make it pass 'use strict' and -w. I get a whole bunch of errors of 'Argument "" isn't numeric in formline at t.pl line 42'.

      Update #1: I, too, have modified this code to reflect merlyn's change. However, I still get the same error message...

      Update #2: It was determined that using the original format code wasn't working because the @### doesn't work with ~~, since you can't get an empty string. Changing these to <'s fixed it.

      But, I don't know jack about formats, so I can't fix it. Any thoughts? And what version of Perl are you running in your head? 5.005_03, or 5.6? <G> 
      #!/usr/local/bin/perl -w

use strict;

my %hash_you_want_to_scan = ('kudra'      => 1, 
                             'neshura'    => 2, 
                             'Ozymandias' => 3,
                             'merlyn'     => 4,
                            );
                            
{
  my $value;
  my $hash_ref;
  my $done;
  
  sub get_key {
    my $key;

    unless ($done) {
      ($key, $value) = each %$hash_ref or # yes, $value is out of scop
+e
        $done = 1;
    }
    defined $key ? $key : "";
  }
  
  sub get_value {
    defined $value ? $value : "";
  }
  
  sub set_hash {
    $hash_ref = shift;
    keys %$hash_ref; # reset each()
    $done = 0;
  }
}

set_hash(\%hash_you_want_to_scan);
write STDOUT;

format STDOUT =
@<<<<< @<<<     @<<<<< @<<< ~~
get_key(), get_value(), get_key(), get_value()
.

      [download]
      Original code that merlyn identified as broke was: 
        sub get_key {
    my $key;
    unless ($done) {
      ($key, my $value) = each %$hash_ref or # yes, $value is out of s
+cope
        $done = 1;
    }
    defined $key ? $key : "";
  }

      [download]
      (It's the extra 'my' in front of the $value, which was wrecking the scope).
      Original format that caused the runaway format error: 
      format STDOUT =
@>>>>> @###     @>>>>> @### ~~
get_key(), get_value(), get_key(), get_value()
.

      [download]


      --Chris

      e-mail jcwren
[reply]
[d/l]
[select]
        You broke it. Leave it the way I wrote it, and try again. The $key is getting my'ed in that line. The $value is going into the next outer scope. I even said that in the comment!

        -- Randal L. Schwartz, Perl hacker

[reply]

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